Optical device and three-dimensional display device

ABSTRACT

An optical device includes a transparent material layer having a desired curved surface configuration, a layer including a variable refractive index material having a dielectric constant anisotropy, at least two transparent electrodes arranged to sandwich the transparent material layer and the variable refractive index material, and a driving device supplying a voltage including driving frequencies f 1  and f 2  between the transparent electrodes. The difference Δ∈ in the dielectric constant of the variable refractive index material due to the anisotropy is positive at one of the driving frequencies and negative at the other driving frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.10/011,638 filed Dec. 11, 2001 now U.S. Pat. No. 6,714,174, which is adivisional application of application Ser. No. 08/784,353, filed on Jan.16, 1997 now U.S. Pat. No. 6,469,683. The disclosure of theabove-referenced patent applications, as well as that of each U.S. andforeign patent and patent application identified in the specification ofthe present application, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device which canperiodically or sequentially vary an optical property of the opticaldevice, such as the focal length of a lens, the deflection angle of aprism, the divergence angle of a lenticular lens and so on.

Further, the present invention relates to a three-dimensional displaydevice and its driving method. More specifically, the present inventionrelates to a technology effectively applicable to an apparatus fordisplaying a two-dimensional image to be displayed on a two-dimensionaldisplay device in a three-dimensional fashion.

2. Description of the Related Art

Most of the conventional optical devices are passive optical devices.The kinds of active optical devices whose optical properties can bevaried by voltage or the like are quite limited. Amongst them, as anoptical device employing a material having a variable refractive index,there is a liquid crystal lens disclosed in Science Research ExpenditureSubsidy Research Results Report No. 59850048 (1984).

FIG. 1 shows the construction of such a liquid crystal lens. The liquidcrystal lens having optical properties to be varied by voltage or thelike shown in FIG. 1 is constructed with a planar convex lens 1 formedof a polymer, glass or the like, a transparent electrode formed on thesurface of the planar concave lens 1, an alignment layer formed of apolyimide or the like on the transparent electrode 2, a liquid crystal 4(ordinary nematic liquid crystal having an anisotropy of its dielectricconstant which is not reversed by difference of frequency), an oppositesubstrate 5 opposite to these components, a transparent electrode 6formed on the opposite substrate 5, an alignment layer 7 formed ofpolyimide or the like on the transparent electrode 6, and a drivingdevice for driving these components. Here, the alignment layers 3 and 7are in a homogeneous alignment condition for aligning the liquid crystal4 substantially in parallel.

In the condition where no voltage is applied between the transparentelectrodes 2 and 6, the liquid crystal 4 is aligned to be substantiallyparallel to the alignment layers 3 and 7 by the action of the alignmentlayers 3 and 7. In this case, an incident light beam 11 that ispolarized parallel to the alignment direction is subject to anextraordinary refractive index of the liquid crystal 4. Thus, forexample, the liquid crystal 4 appears to have a large refractive indexin comparison with the planar concave lens 1 so that the entire opticaldevice serves as a planar convex lens to cause convergence as an outputlight beam 12.

On the other hand, in the condition where an appropriate voltage isapplied between the transparent electrodes 2 and 6, the liquid crystal 4is aligned to be perpendicular to the electrode 2 and 6. In this case,the incident light beam 11 is subject to the ordinary refraction of theliquid crystal 4. Therefore, for example, the liquid crystal 4 appearsto have substantially the same refractive index as the planar concavelens. Then, the entire optical device merely serves as glass plate tooutput a light beam 13 having substantially the same direction as theincident light beam 11.

Even in such a conventional optical device, it has been possible tosequentially vary an optical property, e.g. focal length, of the planarconvex lens depending upon an applied voltage. One example of thisrelationship is illustrated in FIG. 2.

However, the conventional optical device has the following detects.Alignment of the liquid crystal 4 in the condition where no voltage isapplied, is performed only by an anchoring force of the alignment layers3 and 7. In such a optical device, since the liquid crystal 4 has alarge thickness of several hundreds μm or more, a drawback has beenencountered in that a resumption timing upon driving is delayedsignificantly by several seconds, as shown in FIG. 3. Furthermore, evenif the applied voltage is increased, the resumption timing can be hardlyimproved. Therefore, currently, there is no effective method forshortening a resumption period.

As set forth above, when the liquid crystal 4 is aligned only by theanchoring force of the alignment layers 3 and 7, molecules 4 a of theliquid crystal 4 may be aligned along a curved surface of the planerconcave lens in a portion located in the vicinity of the transparentelectrode 2, as shown in FIG. 4. Therefore, alignment of a part of theliquid crystal tends to be inclined, so that the refractive index to besensed by the incident light beam becomes closer to the refractive indexof the planar concave lens, thereby making the amount of variation ofthe optical property smaller. Furthermore, there is a disadvantage inthat distribution of the variation amount of the optical propertydepends on the position with respect to the lens.

Further, since the transparent electrode 2 is formed on the surface ofthe planar concave lens 1, when the voltage is applied, an electricfield perpendicular to its surface is established in the vicinity of thetransparent electrode 2 so that the liquid crystal 4 may be alignedperpendicularly to the surface thereof. As a result, there arises aninclination of the alignment of a part of the liquid crystal 4 to form aregion where the refractive index sensed by the incident light beam issignificantly different from the refractive index of the planar concavelens 1. Thus, the incident light beam which should pass through withoutany deflection substantially, is locally deflected.

Furthermore, in the case where the surface configuration of the planarconcave lens 1 is more complicated, particularly when it has deepgrooves or sharp projections, it becomes difficult to uniformly form thetransparent electrode, so that a circuit breakage or high resistance isliable to occur.

Additionally, in such case, an alignment process of the alignment layersfor aligning the liquid crystal, such as a rubbing process and the like,becomes difficult. Further, the distance between the transparentelectrodes varies at different positions as is clear from FIG. 1.Despite this fact, since an equal voltage is applied to all positions ofthe transparent electrodes, degradation of insulation, short circuits,etc. are liable to occur in a narrow region.

As set forth above, the conventional active optical device employing amaterial having a variable refractive index encounters various practicaldrawbacks or shortcoming in production and driving.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical devicewhich can be driven at high speed, achieves high uniformity, is easy tofabricate, and can vary an optical property sequentially, periodicallyin an active manner.

According to the present invention, there is an optical devicecomprising:

a transparent material layer having a desired curved surfaceconfiguration;

a layer including a variable refractive index material having adielectric constant anisotropy and having a property in which a sign ofa difference Δ∈ in dielectric constant due to the anisotropy is reversedat driving frequencies f1 and f2;

at least two transparent electrodes arranged to sandwich the transparentmaterial layer and the layer including the variable refractive indexmaterial; and a driving device supplying a voltage including the drivingfrequencies f1 and f2 between the transparent electrodes.

The optical device according to the invention enables high speedoperation by varying the refractive index by varying the frequency of avoltage which is applied to the variable refractive index material inorder to vary an optical property of the device. Furthermore, since theforce of the electric field can be always used, the speed can be madehigher by increasing the electric field.

In addition, in the optical device according to the invention, the forceof the electric field can be varied by the variable refractive indexmaterial, and since the transparent electrodes are not provided on theside of the variable refractive index material of the transparentmaterial layer, the optical device is hardly influenced by the surfaceconfiguration of the transparent material layer, compared to the priorart device, regardless of the condition of the variable refractive indexmaterial. Therefore the amount of variation of the optical property canbe easily made uniform. Since the transparent electrodes are notprovided on the side of the variable refractive index material of thetransparent material layer in the optical device according to thepresent invention, it becomes unnecessary to form a film to meet theshape of a complicated surface configuration to facilitate fabricationof the optical device, compared to the prior art device. Furthermore,since the transparent electrodes are not provided on the side of thevariable refractive index material of the transparent material layer,the distance between the transparent electrodes can be maintainedsubstantially the same, and the transparent material layer is alwayspresent between the transparent electrodes, degradation of insulation,shorts, and so on hardly occur.

Further, by replacing one of the transparent electrodes with anelectrode reflecting at least a part of the incident light beam, anactive mirror, half mirror or various other types of optical devices forvarying an optical property can be realized.

According to the present invention, there is an optical devicecomprising:

a layer including a variable refractive index material having dielectricconstant anisotropy and having a property to reverse signs of adifference of dielectric constant Δ∈ due to anisotropy at drivingfrequencies f1 and f2;

at least two transparent electrodes arranged to sandwich the layerincluding the variable refractive index material; and

a driving device applying a voltage, in which voltages from V1 to VNrespectively having respective primary frequencies f1 to fN (N≧2) aresuperimposed, between the transparent electrodes.

According to the present invention, there is an optical devicecomprising:

a layer of transparent material having a desired curved surfaceconfiguration;

a layer including a variable refractive index material having a positiveor negative dielectric constant anisotropy;

at least two transparent electrodes arranged to sandwich the layer ofthe transparent material and the layer including the variable refractiveindex material; and a driving device for always supplying a voltagesubstantially equal to or greater than an amplitude of a voltageestablishing static and vertical alignment in the variable refractiveindex material.

As set forth above, the optical device according to the presentinvention has a driving device which can always supply the voltagehaving an amplitude equal to or greater than the voltage, at which thevariable refractive index material is statistically aligned to generateelectrofluid motion in the molecules of the liquid crystal to change therefractive index of the variable refractive index material in such a waythat the orientation of the liquid crystal molecules vary in synchronismwith a frequency twice that of the frequency of the voltage applied,between the state where the orientation of the liquid crystal moleculesis perpendicular or parallel to the electrode and the state where theorientation of the liquid crystal molecules is slightly inclined fromthe former state. Therefore, the optical device according to the presentinvention can vary the optical property at a high speed, sequentially,periodically and uniformly. Furthermore, it becomes unnecessary toprocess the film to meet a complicated surface configuration, and thefabrication can be facilitated.

According to the present invention, there is a three-dimensional displaydevice for forming a three-dimensional image from two-dimensional imageson a display portion, comprising:

a layer of a transparent material having a desired curved surfaceconfiguration;

a layer of a variable refractive index material having a refractiveindex varying in accordance with a voltage applied thereto;

at least two transparent electrodes arranged to sandwich the layer ofthe transparent material and the layer including the variable refractiveindex material;

an imaging position shifting portion for shifting an imaging position ofthe two-dimensional image displayed on the display portion;

a synchronizing portion for synchronizing an updating period of thetwo-dimensional image displayed on the display portion with a shiftingperiod of the imaging point of the imaging position shifting portion;and

a driving portion for driving the imaging point shifting portion byapplying a voltage to the at least two transparent electrodes inaccordance with an output from the synchronizing portion.

The three-dimensional display device according to the present inventiondecomposes the three-dimensional image into two-dimensional images(depth sample images) belonging to planes set at a predeterminedinterval in a depth direction of an image pick-up position fordisplaying the images in a predetermined sequence on the displayportion, and the imaging position of the image to be displayed on thedisplay portion is varied by the imaging portion shifting portion. Here,the image displayed on the display portion and the imaging position aresynchronized by the synchronizing portion so that the observer may viewthe image displayed on the display portion as a three-dimensional image.

According to the present invention, there is a driving method of drivinga three-dimensional display device including a display portion fordisplaying two-dimensional images, an imaging point shifting portiondisposed between the display portion and an observer, a synchronizingportion for synchronizing an updating period of the two-dimensionalimages displayed on the display portion with a shifting period of theimaging point of the imaging point shifting portion, and a drivingportion for driving the imaging point shifting portion, the a drivingmethod comprising the steps of:

outputting a plurality of driving signals of an output voltage VN (N≧2)having frequency fN as a primary frequency for a predetermined period oftime assigned to each of the driving signals in a predetermined sequenceto drive the imaging point shifting portion in the driving portion; and

updating and displaying the two-dimensional images in a predeterminedsequence on the display portion in the synchronizing portion.

According to the present invention, there is a driving method of drivinga three-dimensional display device including a display portion fordisplaying two-dimensional images, an imaging point shifting portiondisposed between the display portion and an observer, a synchronizingportion for synchronizing an updating period of the two-dimensionalimages displayed on the display portion with a shifting period of theimaging point of the imaging point shifting portion, and a drivingportion for driving the imaging point shifting portion, the a drivingmethod comprising the steps of

in the driving portion:

generating a driving signal of a predetermined output voltage in which afrequency fN (N≧2) is superimposed;

applying the driving signal to the imaging position shifting portion;

varying the output voltage in a predetermined sequence in accordancewith a synchronization signal of the synchronizing portion; and

in the synchronization portion:

outputting a synchronization signal in the synchronization portion whenupdating two-dimensional images to be displayed on the display portion.

In the foregoing three-dimensional display device, there appears aphantom image of the image on the back side or inside which should behidden. Therefore, it can be useful only for reproducing a wire framelike three-dimensional image, in practice. The invention makes itpossible to display the real three-dimensional image display in thiscase.

According to the present invention, there is a three-dimensional displaydevice comprising:

a phantom three-dimensional display device for displaying a phantomthree-dimensional image; and

a shutter device formed by a shutter element for controlling a lighttransmittance, the shutter device being located at a position where thephantom three-dimensional image is reproduced or a position opticallyequivalent to the position. According to the three-dimensional displaydevice, the shutter element of the shutter device, interputs theincident light beam or scatters the light beam while the phantom imageon the back side as viewed from the observer is being reproduced. Bythis display device, many of the visual cues to depth perception can besatisfied and the natural three-dimensional image with no phantomphenomenon can be reproduced in the form of motion picture.

According to the present invention, there is a three-dimensional displaydevice comprising:

a phantom three-dimensional display device for displaying a phantomthree-dimensional image; and

a shutter device formed by a shutter element for controlling a lighttransmittance,

the phantom three-dimensional image being a real image, and the shutterelement being a photoreactive element for lowering a light transmittancein a real image region at the position of the shutter element inaccordance with an imaging light beam of the real image.

According to the present invention, there is a head-mount display devicecomprising:

two display devices corresponding to left and right eyes and eachincluding a two-dimensional display device and an optical device havinga variable focal length; and

a control device for controlling the two-dimensional display device andthe optical device having a variable focal length,

the display devices being mounted to left and right eyes, and thecontrol device synchronously driving the two-dimensional display deviceand the optical device to perform three-dimensional display.

The head-mount display device according to the present invention is wornon respective left and right eyes of a human being so that the humanbeing or viewer can view display images on the two-dimensional displaydevices through the optical device of variable focal length. Then, byvarying the focal length of the optical device, the virtual imageposition of the display image of the two-dimensional display device isvaried in the depth direction. According to this display device, visualcues to depth perception, such as binocular disparity, convergence, andfocus of the eyes in stereoscopy can be satisfied with no discrepancyand the natural three-dimensional image with no phantom phenomenon canbe reproduced at a high speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to be eliminative to the present invention, but are forexplanation and understanding only.

In the drawings:

FIG. 1 is an illustration showing the construction of one example of aconventional liquid crystal lens;

FIG. 2 is a chart showing the relationship between the focal length andan applied voltage in the device of FIG. 1;

FIG. 3 is a chart showing the relationship between a reaction period andan applied voltage in the device of FIG. 1;

FIG. 4 is a conceptual illustration showing the alignment of liquidcrystal molecules by an anchoring force of an alignment layer in thedevice of FIG. 1;

FIG. 5 is a conceptual illustration of alignment of the liquid crystalmolecules upon charging of voltage in the device of FIG. 1;

FIG. 6 is an illustration showing the construction of the firstembodiment of an optical device according to the present invention;

FIG. 7 is a chart showing the relationship between the dielectricconstant of the liquid crystal of FIG. 6 and the frequency of a drivingvoltage;

FIG. 8 illustrates suitable waveforms for the driving voltage of theoptical device of FIG. 6;

FIG. 9 is an explanatory illustration showing sequential periodic motionof the liquid crystal of FIG. 6;

FIG. 10 is a graph showing a plane distribution of brightness of anoutput light beam;

FIGS. 11A and 11B are charts illustrating other waveforms for thedriving voltage of FIG. 6;

FIG. 12 is an illustration showing a matrix apparatus employing theoptical device according to the present invention;

FIG. 13 is an illustration showing a modification of the firstembodiment of the optical device of the present invention;

FIG. 14 is an illustration showing another modification of the firstembodiment of the optical device of the present invention;

FIG. 15 is an illustration showing another modification of the firstembodiment of the optical device of the present invention;

FIG. 16 is an illustration showing another modification of the firstembodiment of the optical device of the present invention;

FIG. 17 is an illustration showing another modification of the firstembodiment of the optical device of the present invention;

FIG. 18 is an illustration showing another modification of the firstembodiment of the optical device of the present invention;

FIG. 19 is an illustration showing the second embodiment of the opticaldevice according to the present invention;

FIG. 20 is an illustration showing a construction employing the opticaldevice of FIG. 19;

FIG. 21 is an illustration showing the third embodiment of the opticaldevice according to the present invention;

FIG. 22 illustrates suitable waveforms for the driving voltage for thedevices of FIGS. 13-19 and FIG. 21;

FIG. 23 illustrates suitable waveforms for another driving voltage forthe devices of FIGS. 13-19 and FIG. 21;

FIG. 24 is an illustration showing a modification of the thirdembodiment of the present invention;

FIG. 25 is an explanatory illustration showing sequential variations ofan optical property in the third embodiment of the optical deviceaccording to the present invention;

FIGS. 26A and 26B are waveforms of a driving voltage for explaining thethird embodiment of the optical device according to the presentinvention;

FIG. 27 is an illustration showing the fourth embodiment of the opticaldevice according to the present invention;

FIG. 28 is an illustration showing a modification of the fourthembodiment of the optical device according to the present invention;

FIG. 29 is an illustration showing another modification of the fourthembodiment of the optical device according to the present invention;

FIG. 30 is a chart showing the relationship between the driving voltagefor the optical device and the deflection angle;

FIG. 31 is a chart illustrating the relationship between the appliedvoltage and the deflection angle for explaining another driving methodof the optical device according to the present invention;

FIGS. 32A and 32B are charts illustrating a detailed relationshipbetween the applied voltage and the deflection angle of FIG. 31;

FIGS. 33 to 37 are charts illustrating other relationships between theapplied voltage and the deflection angle;

FIG. 38 is a block diagram schematically showing the construction of athree-dimensional display device employing conventional liquid crystalshutter eyeglasses;

FIG. 39 is a block diagram schematically showing the construction of athree-dimensional display device employing a conventional lenticularlens sheet;

FIG. 40 is a block diagram schematically showing the construction of afirst embodiment of a three-dimensional display device according to thepresent invention;

FIG. 41 is a graph illustrating how focal length varies when a varifocallens is driven by the driving device of the first embodiment of thethree-dimensional display device according to the present invention;

FIGS. 42A and 42B are views for explaining the operation of the firstembodiment of the three-dimensional display device;

FIG. 43 is a block diagram schematically showing the construction of asecond embodiment of the three-dimensional display device according tothe present invention;

FIG. 44 is an illustration for explaining the second embodiment of thethree-dimensional display device;

FIG. 45 is a block diagram schematically illustrating the constructionof a third embodiment of the three-dimensional display device accordingto the invention;

FIG. 46 is a view schematically showing the construction of a varifocallens of the three-dimensional display device;

FIG. 47 is a view schematically showing the construction of anotherembodiment of the three-dimensional display device;

FIG. 48 is an illustration showing a motion speed of an image by thevarifocal lens;

FIG. 49 is a view schematically showing the construction of a fourthembodiment of the three-dimensional display device according to thepresent invention;

FIG. 50 is an illustration showing the basic operation of the fourthembodiment of the three-dimensional display device;

FIG. 51 is a view schematically showing the construction of a fifthembodiment of the three-dimensional display device according to thepresent invention;

FIG. 52 is an illustration showing the basic operation of the fifthembodiment of the three-dimensional display device;

FIG. 53 is a view schematically showing the construction of a sixthembodiment of the three-dimensional display device according to thepresent invention;

FIG. 54 is an illustration showing the basic operation of the sixthembodiment of the three-dimensional display device;

FIG. 55 is a view schematically showing the construction of the sixthembodiment of the three-dimensional display device employing an opticalsystem such as a lens or a mirror;

FIGS. 56A to 58 are sections showing embodiments of shutter devices inthe three-dimensional display device;

FIG. 59 is an illustration showing the basic operation of a seventhembodiment of the three-dimensional display device;

FIG. 60 is a perspective view showing a first embodiment of a head-mountdisplay device;

FIG. 61 is a plan view of the device of FIG. 60, on a plane includingthe eyes of an observer;

FIGS. 62 and 63 are views showing the basic operation of the firstembodiment of the head-mount display device;

FIG. 64 is a graph illustrating visual cues to depth perception;

FIG. 65 is a graph illustrating the correspondence and allowable rangeof convergence and accommodation;

FIG. 66 is a view schematically showing the construction of a secondembodiment of the headmount display device; and

FIG. 67 is a view schematically showing the construction of amodification of the second embodiment of the head-mount display device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinafter in detail by way ofthe preferred embodiments of the present invention with reference to theaccompanying drawings. In the following descriptions, numerous specificdetails are set forth in order to provide thorough understanding of thepresent invention. It will be obvious, however, to those skilled in theart that the present invention may be practiced without these specificdetails. In other instance, well-known structures are not shown indetail in order to avoid unnecessarily obscuring the present invention.

At first, the preferred embodiments of an optical device according tothe present invention will be discussed hereinafter. While thedescriptions will be given hereinafter by way of embodiments mainlyemploying a fresnel lens structure as a surface of a layer of atransparent material, it is evident that similar effects should beexpected in the case of a convex lens, a concave lens, a prism array, alens array, a lenticular lens, a diffraction grating or combinationsthereof.

The embodiments set forth hereinafter mainly employ a liquid crystal asa variable refractive index material, but equivalent effects should beexpected even when other material having frequency dependency inanisotropy of dielectric constant is used.

Furthermore, in the following embodiments the refractive index of liquidcrystal is substantially equal to that of the transparent material whenthe liquid crystal is aligned substantially perpendicular to atransparent electrode. However, evidently, similar effects should beexpected even when the refractive index of a liquid crystal issubstantially equal to that of the transparent material when the liquidcrystal is aligned substantially parallel to the transparent electrodeor when the liquid crystal is aligned at a given angle with thetransparent electrode.

Furthermore, in the following embodiments, the refractive index of theliquid crystal is substantially greater than that of the transparentmaterial, but it is clearly possible to expect similar effects even inthe case where the refractive index of the liquid crystal issubstantially smaller than that of the transparent material or the casewhere the refractive index of the transparent material falls within avariation range of the refractive index of the liquid crystal.

(First Embodiment of the Optical Device)

FIG. 6 shows one embodiment of the optical device according to thepresent invention. In FIG. 6, the optical device comprises a layer 21 ofa transparent material having a desired curved surface configuration andformed of a transparent polymer, glass or the like, a variablerefractive index material 22 formed of a transparent material or thelike including a liquid crystal, a plurality of transparent electrodes23 and 24 sandwiching the transparent material layer 21 and a layerincluding the variable refractive index material 22 and formed of ITO orSnOx, and a driving device 25 for driving these molecules.

Here, if it is intended to provide a planar convex lens with a variablefocal length (focal length is positive) as an active optical device, andif the refractive index of the variable refractive index material 22 issubstantially greater than the refractive index of the transparentmaterial layer 21, the variable refractive index material 22 may beformed in the shape of a convex lens. Accordingly, the surfaceconfiguration of the transparent material layer 21 on the side of thevariable refractive index material 22 may be formed in a concave fresnellens shape as illustrated. Of course, when the refractive index of thevariable refractive index material 22 is substantially smaller than therefractive index of the transparent material layer 21, the surfaceconfiguration of the transparent material layer 21 on the variablerefractive index material 22 side may be in the form of a convex fresnellens, for example.

In this embodiment, the variable refractive index material 22 has arefractive index anisotropy and a dielectric constant anisotropy. Thisembodiment uses an example in which the dielectric constant anisotropyΔ∈ (=0∥ (dielectric constant in parallel to a longer axis of themolecule)−0⊥ (dielectric constant in a direction perpendicular to thelonger axis of the molecule)) is positive at a frequency f11, and thedielectric constant anisotropy Δ∈ is negative at a frequency f12.Further, this embodiment uses an example in which the refractive indexanisotropy n_(o) (ordinary refractive index) is substantially equal tothe refractive index of the transparent material layer 21, and n_(e),(extraordinary refractive index) is substantially greater than therefractive index of the transparent material layer 21.

When an electric field having a frequency f11 is applied between thetransparent electrodes 23 and 24 from the driving device 25, Δ∈>0.Consequently, the molecules of the variable refractive index material 22are aligned in parallel to the direction of the electric field, namely,perpendicular to the transparent electrodes 23 and 24. Therefore, inview of the relationship between the transparent material layer 21 andthe variable refractive index material 22, the refractive index of thevariable refractive index material 22 becomes substantially equal to therefractive index of the transparent material layer 21. Consequently, thelight beam 26 incident into the optical device passes substantiallywithout any variation, as output light beam 27.

On the other hand, when an electric field having a frequency f12 isapplied between the transparent electrodes 23 and 24 from the drivingdevice 25, Δ∈<0. Consequently, the elements of the variable refractiveindex material 22 are aligned perpendicular to the direction of theelectric field, namely parallel to the transparent electrodes 23 and 24.Therefore, in view of the relationship between the transparent materiallayer 21 and the variable refractive index material 22, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 21. In effect,the variable refractive index material 22 becomes a convex fresnel lens.The optical device according to this embodiment serves as a convexfresnel lens for an incident light beam 26 as a polarized light beamparallel to the longer axis of the molecules of the variable refractiveindex material 22, and converges as a output light beam 28.

In this embodiment, the focal length of the lens is an optical propertyof the optical device that can be varied by varying the refractive indexof the variable refractive index material 22.

In this embodiment, unlike the prior art shown in FIGS. 1 to 5, a forceexerted by the electric field 10 is mainly utilized by varying thealignment of the variable refractive index material 22 depending upondifference of the frequency of the applied voltage. Therefore, byincreasing the intensity of the electric field, the variation speed canbe extremely increased.

Further, the alignment of the variable refractive index material 22 isvaried by the force exerted by the electric field, and the transparentelectrode 23 is not provided on the transparent material layer 21 on theside of the variable refractive index material 22. Therefore, in eitheralignment condition of the variable refractive index material 22, theinfluence of the surface

configuration of the transparent material layer 21 becomes much smallerthan that in the prior art shown in FIGS. 1 to 5, facilitating uniformvariation of the focal length.

Since the transparent electrode 23 is not provided on the transparentmaterial layer 21 on the side of the variable refractive index material22, it becomes unnecessary to form a layer on a portion having acomplicate configuration, thus facilitating the fabrication process to agreater degree than the prior art illustrated in FIGS. 1 to 5.

Furthermore, since the transparent electrode 23 is not provided on thetransparent material layer 21 on the side of the variable refractiveindex material 22, it becomes easy to set the distance between thetransparent electrodes 23 and 24 substantially equal. In addition, sincethe transparent material layer 21 is always present between thetransparent electrodes 23 and 24, degradation of insulation,short-circuiting or the like which are liable to occur in the prior artof FIGS. 1 to 5, can be successfully avoided.

As set forth above, the refractive index of the transparent materiallayer and the ordinary refractive index (or extraordinary refractiveindex) of the variable refractive index material, such as liquid crystalor the like, are set to be substantially equal to each other, but thisis not necessarily required. Namely, setting the refractive indexingsubstantially equal corresponds to setting the focal length close toinfinite. However, if it is difficult to set the refractive indexes atsubstantially equal values from the viewpoint of materials, or ifmaterials which allow setting of the refractive indexes at substantiallyequal values cannot be employed in relation with other physicalproperties (dielectric constant anisotropy, refractive index anisotropy,temperature characteristics, mixing ability with catalyst, toxicity andso forth), it may be possible to set the focal length close to infiniteby a correction made by arranging a fixed focus lens at the front orback side of the device.

Thus, this embodiment can increase the driving speed in comparison withthe prior art, provides superior uniformity, easiness of fabrication,and thus can solve the problems in driving.

FIGS. 7 to 12 show an embodiment employing a nematic liquid crystal asone example of the optical device according to the present invention.

Here, as a material showing dielectric constant anisotropy dependingupon the frequency, such as the variable refractive index materialemployed in the present invention, there is a dual-frequency liquidcrystal among the nematic liquid crystals.

FIG. 7 shows a specific example of the driving frequency dependency ofthe dielectric constant anisotropy Δ∈(=0μ−0⊥) of the dual-frequencyliquid crystal. The example of the nematic liquid crystal shown hereinis Δ∈>0 at a low frequency, As becomes smaller gradually as thefrequency becomes higher, and Δ∈<0 at a high frequency range. Here, whenΔ∈>0, the longer axes of the molecules of the dual-frequency liquidcrystal are aligned along the electric field, and when Δ∈<0, the longeraxes of the molecules of the dual-frequency liquid crystal are alignedperpendicularly to the electric field. Accordingly, by simply varyingthe frequency, the refractive index of the dual-frequency liquid crystalcan be varied in a substantially binary manner (n_(o) and n_(e)), andthus the refractive index cannot be varied sequentially. (It should benoted that it may be possible to vary the refractive index by a balanceof the anchoring force of the alignment layer and the force of theelectric field, but this may encounter various problems as pointed outin the prior art.)

FIG. 8 illustrates one example of a waveform of the driving voltagewhich can periodically vary the refractive index of the dual-frequencyliquid crystal sequentially. An example is shown in which twofrequencies f11 (Δ∈>0) and f12 (Δ∈<0), at which Δ∈ has different signs,are used. In the driving method in this embodiment, a voltage having aprimary frequency at f11 and a voltage having an equal amplitude to theformer voltage and having a primary frequency at f12 are applied at agiven duty ratio and a given period.

When driven in this manner, the molecules of the dual-frequency liquidcrystal sense and respond to a force for aligning the longer axes of themolecules along the electric field (upon application of the frequencyf11) and to a force for aligning the longer axes of the moleculesperpendicular to the electric field (upon application the frequency f12)periodically, alternately.

If there were no other constraint, the liquid crystal should abruptlyvary at a switching point between the frequencies f11 and f12 andpractical analogue operation would not be possible. However, inpractice, there are constraints, such as viscosity, and such constraintsmay balance with the periodically alternating force to permit uniformanalogue periodic aligning motions at a high speed over a wide range.

It should be appreciated that, in this driving method, it is importantto periodically apply the electric fields at f11 and f12 for a givenperiod of time. If the electric fields at frequency f11 and frequencyf12 are applied one time only, uniformity may be degraded or divergencemay be increased to reduce the practicality of the arrangement as avarifocal lens. By periodically applying the frequency f11 and thefrequency f12 respectively for a given period, the foregoing balance maybe established, and uniform operation over a wide range becomespossible.

FIG. 9 shows one example of periodical sequential motions of the liquidcrystal. Here, a prism shape is employed as the surface configuration ofthe transparent material layer in the device illustrated in FIG. 6.

Further, as driving frequencies, a low frequency f11 and a highfrequency f12 are used for driving, with rectangular waveforms as shownin FIG. 8. In this case, when the liquid crystal is alignedperpendicularly to the transparent electrode, the refractive index ofthe liquid crystal and the refractive index of the transparent materialare substantially equal to each other. When the liquid crystal isaligned substantially parallel to the transparent electrode, therefractive index of the liquid crystal becomes greater than therefractive index of the transparent material. In FIG. 9, the horizontalaxis represents a time from a timing of the beginning of the highfrequency f12 (standardized by a repetition period of f11 and f12), andthe vertical axis represents an output light beam variation angle(degree) caused by a variation of the refractive index.

It becomes clear from FIG. 9 that as the phase increases, the variationangle of the incident light beam shows behavior close to a sine wave andthus can be varied analogously. Further, the repetition period of twofrequencies in this example is substantially 20 ms. From this fact, thepresent invention significantly increases a resumption speed incomparison with several seconds achieved by the prior art.

FIG. 10 shows the shape of the output light beam in the former example(instantaneous image at a certain timing). When a circular spot lightbeam is the incident light beam, the output light beam is a spot with asimilar shape at another time point. Since a similar spot image can beobtained at another timing, it becomes clear that the liquid crystal ismaking uniform alignment motions over a wide range.

(Another Driving System of Optical Device)

FIG. 11 shows another example of a waveform for the driving voltagewhich may sequentially vary the refractive index of the liquid crystal.Similarly, as was explained with reference to FIG. 8, two frequenciesf11 (Δ∈<0) and f12 (Δ∈>0) at which Δ∈ has different signs are used inFIG. 11. However, in FIG. 8, the voltages of the frequencies f11 and f12have equal amplitudes and are applied at a given duty ratio andinterval. Here, supply of voltage is temporarily stopped at a desiredphase at an intermediate timing in the interval and subsequentlyresumed.

When supply of the voltage is temporarily stopped, the molecules of thedual-frequency liquid crystal stop at an inclination corresponding tothe stopped phase, and maintain the inclined condition until thisalignment is gradually disturbed by fluctuation due to the anchoringforce of the alignment layer or temperature and so forth. A time elapsesbefore the disturbance of the alignment occurs due to fluctuation due tothe anchoring force of the alignment layer or temperature and so forth.It normally takes several seconds or more. Accordingly, by resuming thevoltage within this time period, the disturbance of the alignment can bekept at a suppressed condition. Furthermore, such small disturbance ofthe alignment can be corrected by resumption of the voltage supply forthe given time period. By driving the liquid crystal in the manner setforth above, it becomes necessary to regularly provide a given refreshtime for correcting the disturbance, but a high speed variation of therefractive index (not necessarily periodic) can be achieved.

(Case in which Optical Devices are Arranged in Matrix)

FIG. 12 shows one example to which the above-described driving method isapplied. FIG. 12 shows a device 32, in which a plurality of cells 31 arearranged in matrix form. As a driving sequence, at first, (1) after agiven period of a refreshing operation (periodic operation shown in FIG.8), (2) voltage supply for respective cells is stopped at phasesrespectively corresponding to the desired variations of the refractiveindexes of respective cells. Then, after the given period in each cell,refreshing operation is resumed. By repeating such manner of driving,the matrix device 32 formed with a plurality of cells can be driven.

Here, the waveform of the driving voltage is not limited to a sine wave.Needless to say, a rectangular wave or saw-tooth wave including thefrequencies f11 and f12 as primary frequencies are also applicable.Further, it is also possible to make the amplitude very periodically.Furthermore, this embodiment employs two frequencies, but a greaternumber of frequencies may be employed as a matter of course.

Since the electric field is the major factor for causing a change in therefractive index in the driving method according to this embodiment, itbecomes possible to further increase the variation in the liquid crystalalignment condition by increasing the amplitude of the applied voltage.Namely, the period of variation of the refractive index in this drivingmethod can be accelerated up to several ms to several tens ms incontrast to several seconds in the prior art. This speed is sufficientlyhigh even when the distance between the transparent electrodes becomesseveral hundreds gm in the construction shown in FIG. 6.

(Modifications of the First Embodiment of the Optical Device)

FIGS. 13 to 18 show modifications of the optical device according to thepresent invention. In these drawings, like portions as in the deviceshown in FIG. 6 will be represented by the same reference numerals.Namely, reference numeral 22 denotes a variable refractive indexmaterial. Reference numerals 23 and 24 denote transparent electrodes.Reference numerals 25 and 41 denote a driving device and a transparentmaterial layer, respectively.

As set forth above, the variable refractive index material 22 hasrefractive index anisotropy and dielectric constant anisotropy. Thedielectric constant anisotropy is that Δ∈>0 at the frequency f11 andΔ∈<0 at the frequency f12. Further, the refractive index anisotropy isthat no (ordinary refractive index) is substantially equal to therefractive index of the transparent material layer 41, and n_(e)(extraordinary refractive index) is substantially greater than therefractive index of the transparent material layer 41.

In the modifications of FIGS. 13 to 18, when a dual-frequency drivennematic liquid crystal is employed as the variable refractive indexmaterial, the driving voltage from the driving device may have thewaveforms shown in FIGS. 7 to 12.

In FIG. 13, the surface configuration of the transparent material layer41 is in a convex lens shape. When the frequency f11 is applied, themolecules of the variable refractive index material 22 are aligned inparallel to the direction of the electric field, namely in a directionperpendicular to the transparent electrodes 23 and 24. Therefore, inview of the relationship between the refractive index of the variablerefractive index material 22 and the refractive index of the transparentmaterial layer 41, the refractive index of the variable refractive indexmaterial 22 becomes substantially equal to the refractive index of thetransparent material layer 41. Accordingly, a light beam 42 incidentinto this device substantially passes therethrough to be outputted asthe output light beam 43 without change.

On the other hand, when frequency f12 is applied, the molecules of thevariable refractive index material 22 are aligned in the directionperpendicular to the electric field, namely in parallel to thetransparent electrodes 23 and 24. Therefore, based upon the relationshipbetween the refractive index of the variable refractive index material22 and the refractive index of the transparent material layer 41, therefractive index of the variable refractive index material 22 becomessubstantially greater than the refractive index of the transparentmaterial layer 41. Here, the variable refractive index material 22becomes a concave lens. Therefore, with respect to the incident lightbeam 42 polarized in parallel to the longer axis of the molecules of thevariable refractive index material 22 of this device, this embodimentserves as a concave lens to cause an output light beam 44.

As set forth above, in the example of FIG. 13, by varying the refractiveindex of the variable refractive index material 22, the focal length ofthe concave lens can be varied.

FIG. 14 shows a further modification of the optical device according tothe present invention. Here is shown an example, in which a transparentmaterial layer 45 having surface configuration in the shape of a concavelens.

When the frequency f11 is applied to this device, the refractive indexof the variable refractive index material 22 becomes substantially equalto the refractive index of the transparent material layer 45 likewise asin the arrangement shown in FIG. 13. Then, the incident light beam 42passes therethrough and is outputted as the output light beam 43 withsubstantially no change.

On the other hand, when the frequency f12 is applied, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 45 as in FIG. 13.Here, since a portion of the variable refractive index material 22 isformed into a convex lens shaped configuration, this embodiment servesas a convex lens with respect to the incident light beam polarized inparallel to the longer axis of the molecule of the variable refractiveindex material 22 to converge the light beam as the output light beam46.

Thus, in the modification of FIG. 14, by varying the refractive index ofthe variable refractive index material 22, the focal length of theconvex lens can be varied.

FIG. 15 shows a still further embodiment of this modification of theoptical device according to the present invention. Here, a transparentmaterial layer 47 having a convex fresnel lens surface configuration isemployed in the arrangement of FIG. 13.

When the frequency f11 is applied to this device, the refractive indexof the variable refractive index material 22 becomes substantially equalto the refractive index of the transparent material layer 47 likewise inFIG. 13. Then, the incident light beam 42 passes therethrough and isoutputted as the output light beam 43 with substantially no change.

On the other hand, when the frequency f12 is applied, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 47 as in FIG. 13.Here, since the variable refractive index material 22 is formed into aconcave fresnel lens shaped configuration, this arrangement serves as aconcave fresnel lens for an incident light beam to diverge the lightbeam so as to provide an output light beam 48.

Thus, in the arrangement of FIG. 15, by varying the refractive index ofthe variable refractive index material 22, the focal length of theconcave fresnel lens can be varied.

FIG. 16 shows a yet further modification of the optical device accordingto the present invention. Here, a transparent material layer 49 having aprism array like surface configuration is employed in the arrangement ofFIG. 13.

When the frequency f11 is applied to this device, the refractive indexof the variable refractive index material 22 becomes substantially equalto the refractive index of the transparent material layer 49 as in FIG.13. Then, the incident light beam 42 passes therethrough and isoutputted as the output light beam 43 with substantially no change.

On the other hand, when the frequency f12 is applied, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 49 as in FIG. 13.With respect to an incident light beam polarized in parallel to thelonger axis of the molecule of the variable refractive index material22, the light beam is deflected depending upon the difference in therefractive indexes and the inclination of the prism to deflect the lightas an output light beam 50.

Thus, in the arrangement of FIG. 16, by varying the refractive index ofthe variable refractive index material 22, the deflection angle can bevaried.

FIG. 17 shows a yet further modification of the optical device accordingto the present invention. Here, a transparent material layer 51 having asurface configuration in the shape of a concave lenticular lens isemployed in the arrangement of FIG. 13.

When the frequency f11 is applied to this device, similarly to theembodiment shown in FIG. 13, the refractive index of the variablerefractive index material 22 becomes substantially equal to therefractive index of the transparent material layer 51. Then, theincident light beam 42 passes therethrough and is outputted as theoutput light beam 43 with substantially no change.

On the other hand, when the frequency f12 is applied, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 51 as in FIG. 13.Here, since the variable refractive index material 22 is formed into theconvex lenticular lens shaped configuration, this arrangement serves asa convex lenticular lens with respect to the incident light beampolarized in parallel to the longer axis of the molecule of the variablerefractive index material 22 to diverge the light beam as an outputlight beam 52.

Thus, in the arrangement of FIG. 17, by varying the refractive index ofthe variable refractive index material 22, the focal length anddiverting angle of the lenticular lens can be varied.

FIG. 18 shows a yet further modification of the optical device accordingto the present invention. Here, a transparent material layer 53 having adiffraction grating like surface configuration is employed in thearrangement of FIG. 13.

When the frequency f11 is applied to this device, the refractive indexof the variable refractive index material 22 becomes substantially equalto the refractive index of the transparent material layer 53 as in thearrangement shown in FIG. 13. Then, the incident light beam 42 passestherethrough and is outputted as the output light beam 43 withsubstantially no change.

On the other hand, when the frequency f12 is applied, the refractiveindex of the variable refractive index material 22 becomes greater thanthe refractive index of the transparent material layer 53 as in FIG. 13.Here, since the variable refractive index material 22 is formed into thediffraction index shaped configuration, this arrangement serves as adiffraction grating with respect to an incident light beam polarized inparallel to the longer axis of the molecules of the variable refractiveindex material 22 to diffract the light beam so as to provide an outputlight beam 54.

Thus, in the arrangement of FIG. 18, by varying the refractive index ofthe variable refractive index material 22, a difference in therefractive index in the diffraction grating can be varied, and thus canvary the intensity of the diffracted light beam.

(Second Embodiment of the Optical Device)

FIG. 19 shows another example of the second embodiment of the opticaldevice according to the present invention. In the drawing, likecomponents as those in the device of FIG. 6 will be denoted by likereference numerals. Namely, reference numeral 21 denotes a transparentmaterial layer, 22 denotes a variable refractive index material, 23 and24 denote transparent electrodes, 25 denotes a driving device, and 61denotes an alignment layer. The alignment layer 61 is formed ofpolyimide, PVA, PVB, inclined evaporation deposition SiO or so forth,and is formed on the surface of the transparent electrode 24 on the sideof the variable refractive index material 22. By processing thealignment layer 61 by the rubbing method or the like, the variablerefractive index material, i.e. the liquid crystal 22 in this case, canbe aligned in a given direction.

By the construction and process set forth above, in the drivingcondition where the liquid crystal 22 is aligned to be parallel to thealignment layer 61, the liquid crystal 22 can be placed in a uniformlyaligned condition in a wide domain region. Because of this, a change inthe refractive index of the liquid crystal 22 can efficiently propagateto the incident light beam. Further, it becomes possible to preventdiverting due to randomly orienting the molecules of liquid crystal 22and opaquing resulting therefrom.

By applying the alignment layer including polyimide, PVA, PVB, inclinedevaporation deposition SiO or so forth on the surface of the transparentmaterial layer 21 on the side of the liquid crystal 22, and providingthe aligning process by a rubbing method and the like, the alignmentability of the liquid crystal 22 on the side of the transparent materiallayer 21 can be improved. Further, when the transparent material layer21 is formed by a replica method (a method for obtaining a replica of adie of metal, glass, plastic or the like), it is possible to directlyalign the liquid in the case of a certain direction of peeling off ofthe replica. In this case, since it becomes unnecessary to apply aspecial layer or to subject the surface having unevenness to thealignment process, fabrication of this device can be facilitated.

Further, by coating a vertical alignment material on the surface of thetransparent material layer 21 on the side of the liquid crystal 22, theliquid crystal 22 on the side of the transparent material layer 21 canbe aligned vertically. The liquid crystal 22 on the side of thetransparent material layer 21 can be aligned to be oriented close tovertical by applying a material containing a group of fluorine or thelike and having a low wettability with the liquid crystal material onthe surface of the transparent material layer 21. In such cases, it issufficient to coat the layer. It is not required to subject a surfacehaving unevenness to the alignment process, so fabrication of thisdevice can be facilitated.

In the optical device shown in FIG. 19, as the variable refractive indexmaterial, a dual-frequency liquid crystal may also be used, for example.With such structure, in the vicinity of the transparent electrode, onwhich the alignment layer is arranged, the molecules of thedual-frequency liquid crystal (variable refractive index material) inthe vicinity thereof can be aligned in a given orientation by carryingout an alignment process such as a rubbing method or the like. However,since no particular alignment process is applied in the vicinity of thetransparent material layer, the alignment orientation of thedual-frequency liquid crystal may differ from one portion to anotherportion so that the variation in the refractive index cannotsatisfactorily propagate to the incident light beam to make it difficultto obtain the effect of varifocal point.

However, even in the case of such construction, by making the light beamincident from the side where the ordering of the liquid crystal hashigher uniformity (e.g. side where the alignment layer is formed), thisproblem can be solved. Namely, by matching the polarized condition ofthe incident light beam with the alignment orientation, variation in therefractive index can effectively propagate to the incident light beam.This is based on the optical rotation property of the liquid crystal.When the alignment orientation of the molecules of the liquid crystal isvaried toward the direction of the incident light beam at a lower speedin comparison with the wavelength, the polarizing direction of theincident light beam is varied following a variation in the alignmentorientation of the molecules of the liquid crystal. (For example, whenthe alignment orientation of the liquid crystal is variedcounterclockwise, the polarizing direction of the incident light beam isalso varied counterclockwise.)

Therefore, even when the alignment orientation is made different fromone position to another position in the vicinity in the transparentmaterial layer, the incident light beam may sufficiently sense thevariation in the refractive index.

Such a construction can dispense with the need to apply a special layeror the need to subject a surface having unevenness to an alignmentprocess, thereby facilitating the fabrication of this device.

FIG. 20 shows an embodiment of the optical device according to theinvention. Namely, reference numerals 71 and 72 denote optical deviceshaving the alignment layer as discussed with respect to FIG. 19. Byarranging the alignment layers in series in a manner such that theymutually intersect each other at right angles substantially, variousfunctions can be achieved irrespective of the polarizing condition ofthe incident light beam.

FIG. 21 shows another embodiment of the optical device according to theinvention. This embodiment of the optical device comprises a variablerefractive index material 81 formed of a transparent material includingliquid crystal, a plurality of transparent electrodes 82 and 83sandwiching the variable refractive index material 81 and formed of ITOor SnOx, and a driving device 84 for driving these components. Here, inthe embodiment of FIG. 21, there is shown one example of the activeoptical device which is directed to providing a device for varying alight beam phase.

In the embodiment of FIG. 21, the variable refractive index material 81has refractive index anisotropy and dielectric constant anisotropy. Thedielectric constant anisotropy, Δ∈(=0∥ (dielectric constant in parallelto the longer axis of the molecule)−(0⊥ (dielectric constant in anorientation perpendicular to the longer axis of the molecule)) ispositive at a frequency f11, and Δs becomes negative at a frequency f12.Further, the refractive index anisotropy, n_(o) (ordinary refractiveindex) is substantially smaller than n, (extraordinary refractiveindex).

When an electric field having a frequency f11 is applied to thetransparent electrodes 83 and 84 by the driving device 84, Δ∈>0. Thus,the molecules of the variable refractive index material 81 are alignedin a direction parallel to the electric field, i.e. in an orientationperpendicular to the transparent electrodes 82 and 83. Therefore, therefractive index of the variable refractive index material 81 becomesn_(o), so that a phase shift associated with the incident light beamoccurs corresponding to a product of the refractive index and thethickness of the layer.

On the other hand, when the driving device 84 applies an electric fieldhaving a frequency f12 to the transparent electrodes 82 and 83, Δ∈<0.Consequently, the molecules of the variable refractive index material 81are aligned perpendicularly to the direction of the electric field,i.e., in parallel to the transparent electrodes 82 and 83. Thus, therefractive index of the variable refractive index material 81 becomesn_(e), which is greater than n_(o). Therefore, the phase shift of theincident light beam 85 becomes greater in comparison with that at thefrequency f11.

In this embodiment described above, by varying the refractive index ofthe variable refractive index material 81, the phase shift of the lightbeam is an optical property of the optical device that can be varied.

(Another Driving Method for an Optical Device)

FIGS. 22 and 23 show examples according to the invention of drivingvoltage waveforms which may be used to sequentially vary the opticalproperty. FIG. 22 illustrates sine waves, while FIG. 23 illustratesrectangular waves. FIG. 22 shows a voltage Vss (in the case of the sinewaves) and FIG. 23 shows a voltage Vrr (in the case of the rectangularwaves). In FIG. 22, Vs1 having a frequency 01 as a primary frequency,and a voltage Vs2 having a frequency 02 as a primary frequency, aresuperimposed at a certain voltage ratio. In FIG. 23, a voltage Vr1having a frequency 01 and a voltage Vr2 having a frequency f32 aresuperimposed at a certain voltage ratio.

By driving with the driving voltages as set forth above, the moleculesof the liquid crystal are simultaneously subject to a force for aligningthe longer axis along the electric field (upon application of thefrequency F31) and a force for aligning the longer axis perpendicular tothe electric field (upon application of the frequency f32) in a ratiocorresponding to the foregoing voltage ratio. Therefore, the moleculesof the variable refractive index material 81 are aligned to be inclinedfrom the electric field direction at an angle where the forces inopposite directions balance. Therefore, the refractive index can bevaried sequentially at high speed. Further, the foregoing action may becombined with the constraining force of the liquid crystal thereby topermit substantially uniform alignment action of the liquid crystal at ahigh speed over a wide domain region.

Here, the waveform of driving voltage is not necessarily a sine wave orrectangular wave and may be a saw-toothed wave containing the foregoingfrequencies f31 and f32 as primary frequencies. Further, it should beclear to provide a variation of the amplitude with time. Furthermore,two frequencies are used in this embodiment, but a greater number offrequencies may also be used.

Since the primary factor influencing the refractive index in thisembodiment of the driving method is the electric field, a higher speedcan be achieved by increasing the amplitude. Namely, even when thedistance between the transparent electrodes is wide, in the order ofseveral hundreds μm, the dual-frequency liquid crystal can vary therefractive index at several tens of milliseconds or less to provide afast response speed.

FIGS. 24 and 25 show one example of the foregoing driving method for theoptical device. In the drawings, like components as in the device ofFIG. 21 will be denoted by the like reference numerals. Namely,reference numeral 81 denotes the variable refractive index material.Reference numerals 82 and 83 denote transparent electrodes. 84 denotesthe driving device and 86 denotes a transparent material layer.

The transparent material layer 86 is formed of a transparent polymer,glass or the like with a desired curved surface configuration anddisposed between the transparent electrodes 82 and 83.

In this embodiment, as one example of the active optical device, aplanar convex lens with a variable focal length (focal length ispositive) is provided. For example, when the refractive index of thevariable refractive index material 81 is substantially greater than therefractive index of the transparent material layer 86, the variablerefractive index material 81 may be formed in the shape of a convexlens. Accordingly, the surface configuration of the transparent materiallayer 86 on the side of the variable refractive index material 81 may bein the shape of a concave fresnel lens. Needless to say, if therefractive index of the variable refractive index material 81 issubstantially smaller than the refractive index of the transparentmaterial layer 86, the surface configuration of the transparent materiallayer 86 on the side of the variable refractive index material 81 may bein the shape of a convex fresnel lens. In this embodiment, the variablerefractive index material 81 has refractive index anisotropy anddielectric constant anisotropy. As the refractive index anisotropy,Δ∈, >0 at the frequency f31 and Δ∈<0 at the frequency f32. Further, inthis embodiment, the dielectric constant anisotropy is such that no issubstantially equal to the refractive index of the transparent materiallayer 86 and ne is substantially greater than the refractive index ofthe transparent material layer 86.

When an electric field having frequency f31 is applied between thetransparent electrodes 82 and 83 from the driving device 84, Δ∈>0.Consequently, the molecules of the variable refractive index material 81are aligned in parallel to the electric field, i.e. in a directionperpendicular to the transparent electrodes 82 and 83. Therefore, fromthe relationship between the refractive indexes of the transparentmaterial layer 86 and the variable refractive index material 81, therefractive index of the variable refractive index material 81 becomessubstantially equal to the refractive index of the transparent materiallayer 86. Accordingly, the light beam incident into this embodiment ofthe optical device according to the invention, may be outputted as anoutput light beam 87 with substantially no change.

On the other hand, when an electric field having frequency f32 isapplied between the transparent electrodes 82 and 83 from the drivingdevice 84, Δ∈<0. Consequently, the molecules of the variable refractiveindex material 81 are aligned perpendicular to the electric field, i.e.in parallel to the transparent electrodes 82 and 83. Therefore, from therelationship between the refractive indexes of the transparent materiallayer 86 and of the variable refractive index material 81, therefractive index of the variable refractive index material 81 becomesgreater than the refractive index of the transparent material layer 86.Here, the variable refractive index material 81 is shaped into a convexfresnel lens. This device serves as a convex fresnel lens with respectto the light beam 85 polarized in parallel to the longer axis of themolecule to make it converge as an output light beam 88.

As set forth above, in this embodiment, the focal length of the lens canbe varied, by varying the refractive index of the variable refractiveindex material 81, amongst the optical properties of the optical device.

However, as set forth above, it is not possible to vary the refractiveindex to an intermediate value between no and ne by simply varying thefrequency.

Sequential variation of the optical property of the optical device canbe obtained by applying the voltage V31 having the frequency f31 as theprimary frequency thereof and the voltage V32 having the frequency f32as the primary frequency thereof in a superimposing manner at a certainvoltage ratio. At this time, the molecules of the dual-frequency liquidcrystal are aligned in an inclined orientation where the forces in theopposite directions are balanced. Further, the constraining force of theliquid crystal is combined with the action set forth above, so thatuniform and high speed alignment operations of the liquid crystal becomepossible, thus enabling uniform variation of the optical property.

FIG. 25 shows one example of a sequential variation in the opticalproperty. In this example, the surface of the transparent material layeris configured in the shape of a prism. The horizontal axis represents avoltage ratio (V32/(V31+V32)) of the voltage V31 having the frequencyf31 as the primary frequency thereof and the voltage V32 having thefrequency f31 as the primary frequency thereof. The vertical axisrepresents a variation of the deflection angle of the output light beamwith a variation in the refractive index (V32/(V31+V32)). From FIG. 25,it is seen that the deflection angle of the output light beam varieswith the increase in the voltage ratio (V32/(V31+V32)). It should benoted that the shape of the output light beam is similar to that of FIG.10. From this, it becomes clear that the liquid crystal makessubstantially uniform alignment actions over a wide range.

Here, the driving voltage to be applied is not necessarily a sine wave.Needless to say, a rectangular wave or saw-tooth wave including thefrequencies f31 and f32 as primary frequencies are also applicable.Further, it is clear that the amplitude may vary with time. Furthermore,this embodiment employs two frequencies, but a greater number offrequencies may be also employed.

Since the electric field is a major factor for causing a variation inthe refractive index in the driving method according to this embodiment,it becomes possible to further accelerate the speed of varying theliquid crystal alignment condition by increasing the amplitude of theapplied voltage. More specifically, a speed of several 10 ms or less asa response speed in the refractive index variation of the dual-frequencyliquid crystal can be achieved even when the distance between thetransparent electrodes reaches several hundreds gym.

Furthermore, since the alignment of the variable refractive indexmaterial 81 is varied by the electric field and the transparentelectrode 82 is not provided on the transparent material layer 86 on theside of the variable refractive index material 81, it becomesunnecessary to form the layer on portions of complicated configuration.Therefore, fabrication can be facilitated in comparison with theconventional device shown in FIGS. 1 to 5.

Furthermore, the transparent electrode 82 is not provided on thetransparent material layer 86 on the side of the variable refractiveindex material 81, so a substantially equal distance between thetransparent electrodes 82 and 83 is maintained over the entire area.Furthermore, the transparent material layer 86 essentially lies betweenthe transparent electrodes 82 and 83, effectively preventing degradationof insulation, short circuits and so forth, unlike the device of FIGS. 1to 5.

As set forth above, in comparison with the prior art, this embodimentcan speed up driving with uniformity, can facilitate fabrication, andsolve the driving problem associated with the prior art.

FIG. 26 shows a further modification according to the invention.

An example is given in which two frequencies f31 (Δ∈>0) and f32 (Δ∈<0)are employed, which result in Δ∈ having different signs, and adual-frequency liquid crystal is used as the variable refractive indexmaterial. Further, sine waves are used in one case and rectangular wavesare used in the other case.

In this embodiment of the driving method, the voltage having thefrequency f31 as the primary frequency and the voltage having thefrequency f32 as the primary frequency are applied in a superimposingmanner at a certain voltage ratio. In addition, the voltage istemporarily stopped at a certain timing and subsequently resumed.

When the voltage is temporarily stopped, the molecules of thedual-frequency liquid crystal stop at an inclination corresponding tothe stopped phase, and maintain the inclined condition until alignmentis gradually disturbed by fluctuation due to the anchoring force of thealignment layer or temperature and so forth. A time period elapsesbefore this disturbance of the alignment occurs due to fluctuation dueto the anchoring force of the alignment layer or temperature and soforth. It normally takes several seconds or more. Accordingly, byresuming voltage within this period, the disturbance of the alignmentcan be maintained as small as possible. Furthermore, such smalldisturbance of the alignment can be corrected by resumption of thevoltage supply for a predetermined interval. By driving the liquidcrystal in the manner set forth above, it becomes necessary to regularlyprovide a given refresh time for correcting disturbance, but a highspeed variation in the refractive index can be achieved whileeliminating the need to constantly apply a voltage.

This driving method is also applicable for the device in which aplurality of cells are arranged in matrix form as shown in FIG. 12. In adriving sequence, at first, (1) after a predetermined interval ofrefreshing operation (shown in FIGS. 22 and 23), (2) voltage supply torespective cells is stopped at phases respectively corresponding to thedesired variation in the refractive indexes of respective cells. Then,after the predetermined interval in each cell, refreshing operation isresumed. By repeating such driving operations, the matrix device 32formed with a plurality of cells can be driven.

Here, the driving voltage to be applied is not necessarily a sine wave.Needless to say, a rectangular wave or saw-tooth wave including thefrequencies f31 and f32 as primary frequencies are also applicable.Further, it is also possible to provide a periodic variation in theamplitude. Furthermore, this embodiment employs two frequencies, but agreater number of frequencies may be employed as a matter of course.

Since the electric field is the major factor for causing the variationin the refractive index in the driving method according to thisembodiment, it becomes possible to further accelerate at the speed ofthe variation in the liquid crystal alignment condition by increasingthe amplitude of the applied voltage. More specifically, the period ofthe variation in the refractive index in this driving method can bespeeded up, exceeding several ms to several tens ms from several secondsas has been conventional. This speed is obtained when the distancebetween the transparent electrodes is as wide as several hundreds gm inthe arrangement shown in FIG. 21. It is evident that such arrangementpermits sufficient speed.

The arrangements shown in FIGS. 13 to 20 as described above may carryout driving operations by applying the driving voltage having thefrequency F31 as the primary frequency and the voltage having thefrequency F32 as the primary frequency in a superimposed manner at acertain voltage ratio as described with respect to FIGS. 22, 23, and 25.Alternatively, the arrangements shown in FIGS. 13 to 20 as describedabove may carry out driving operations by applying the driving voltagehaving the frequency F31 as the primary frequency and the voltage havingthe frequency F32 as the primary frequency in a superimposed manner at acertain voltage ratio and, further, temporarily stopping supply of thevoltage at a certain moment, followed by resuming the supply of thevoltage, as descried with respect to Embodiment 13.

(Fourth Embodiment of the Optical Device)

The foregoing discussions relate to the embodiments in which twoelectrodes for driving the variable refractive index material are bothtransparent electrodes. However, it is advantageous that one of theelectrodes has a mirror surface, in some applications, for example, whenan active mirror varying an optical property, such as the focal length,light beam deflection angle and so forth, is required. This mirror maybe a half mirror.

FIG. 27 shows one embodiment of the optical device according to thepresent invention. In the drawing, like components as in FIG. 6 will beidentified by like reference numerals. Reference numeral 21 denotes thetransparent material layer, 22 denotes a variable refractive indexmaterial, 23 denotes the transparent electrode, and 91 denotes anelectrode.

The electrode 91 has a mirror surface formed in place of the transparentelectrode 24 in the device of FIG. 6. The electrode 91 may be formed ofmetal, such as an aluminum film, chromium film or the like.

In the arrangement set forth above, when the frequency f11 is appliedfrom a driving device, not shown, the refractive index of the variablerefractive index material 22 becomes substantially equal to therefractive index of the transparent material layer 21 as in the firstembodiment. Then, an incident light beam 92 incident from the side ofthe transparent electrode 23 reaches the electrode 91 with nosubstantial variation, and is reflected therefrom to be outputted fromthe transparent electrode 23 as an output light beam 93.

On the other hand, when the frequency f12 is applied, the incident lightbeam is subject to optical effects, such as a lens effect, deflectioneffect and the like depending upon the variation in the refractive indexof the variable refractive index material 22 before reaching theelectrode 91, and is reflected back therefrom to be again subject to thesimilar optical effect to be outputted from the side of the transparentelectrode 23 as an output light beam 94.

Thus, in the embodiment of FIG. 18, by varying the refractive index ofthe variable refractive index material 22, a varifocal mirror or avariable deflection angle mirror can be implemented.

FIG. 28 shows a modification of the optical device. In this embodiment,an electrode 95 formed as a half mirror is used in place of theelectrode 91 in the embodiment of FIG. 27. More specifically, theelectrode 95 has a laminated layer of an ITO film and a metal thin film,a multi-layer film of a metal thin film and an insulation film and soforth, and passes a part of the incident light beam and reflects theremaining part of the incident light beam.

In the arrangement set forth above, when the frequency f11 is appliedfrom a driving device not shown, the refractive index of the variablerefractive index material 22 becomes substantially equal to therefractive index of the transparent material layer 21 as in the firstembodiment. Then, the incident light beam 92 incident from the side ofthe transparent electrode 23 passes through to reach the electrode 95with no substantial variation. A part of the light beam 95 reaching theelectrode 95 passes through the electrode to be outputted as the outputlight beam 96 a, and the remaining part of the light beam 95 isreflected back therefrom to be outputted through the transparentelectrode 23 as an output light beam 96 b.

On the other hand, when the frequency f12 is applied, the incident lightbeam is subject to optical effect, such as a lens effect, deflectioneffect or the like depending upon a variation in the refractive index ofthe variable refractive index material 22 and reaches the electrode 95.Then, a part of the light beam passes through the electrode 95 to beoutputted as an output light beam 97 a, and the remaining part of thelight beam 95 is reflected back therefrom to be again subject to thesimilar optical effect to be outputted through the side of thetransparent electrode 23 as an output light beam 97 b.

Thus, in this modification, by varying the refractive index of thevariable refractive index material 22, a varifocal mirror and a variabledeflection angle transparent optical device can be achievedsimultaneously. Further, when the incident light beam is made incidentfrom the side of the electrode 95, a varifocal lens, a simple mirror anda variable deflection angle transparent optical device can be achievedsimultaneously.

FIG. 29 shows a further modification of the optical device according tothe invention. Here, an electrode 98 formed as a half mirror is employedin place of the transparent electrode 23 in the embodiment shown in FIG.27. More specifically, the electrode 98 has a laminated layer of an ITOfilm and a metal thin film, a mufti-layer film of a thin metal film andan insulation film and so forth, and passes a part of the incident lightbeam and reflects a remaining part of the incident light beam, like theelectrode 95.

In the arrangement set forth above, when the incident light beam 92 ismade incident from the side of the electrode 98, a part of the lightbeam is reflected back from the electrode 98 and a remaining light beamis made incident through the transparent material layer 21 and thevariable refractive index material 22.

At this time, when the frequency f11 is applied from a deriving devicenot shown, the refractive index of the variable refractive indexmaterial 22 becomes substantially equal to the refractive index of thetransparent material layer 21 as in the first embodiment. Then, theincident light beam 92 incident from the side of the transparentelectrode 23 passes through and reaches the electrode 91 with nosubstantial change, and is reflected back therefrom to reach theelectrode 98 again. Then, a part of the reflected light beam is againreflected back from the electrode and the remaining light beam isoutputted. The same process is repeated. However, in this case, sincethe light beam is subject to no optical effect, the output light beam 92becomes merely a reflected light beam.

On the other hand, when the frequency f12 is applied, the incident lightbeam is subject to an optical effect, such as a lens effect, deflectioneffect or the like depending upon a variation in the refractive index ofthe variable refractive index material 22 and reaches the electrode 91,and is reflected back therefrom. The reflected light beam is againsubject to a similar optical effect and reaches the electrode 98. Then,a part of the reflected light beam is reflected back and the remainingis outputted therethrough. The foregoing process is repeated. Wheneverthe process is repeated, the reflected light beam is subject to the sameoptical effect. Therefore, the optical effect becomes greater as thenumber of repetitions becomes greater. Thus, the output light beam 99subjected to the greater optical effect is outputted.

Thus, in this modification, by varying the refractive index of thevariable refractive index material 22, it becomes possible to provide alens having a plurality of focal points and variable focal points,optical devices having a plurality of deflection angles and variabledeflection angles, or the like. At this time, the number of the focalpoints and the deflection angles to be achieved simultaneously can besubstantially determined by adjusting the ratio of passing to reflectingof the electrode 98.

(Another Driving Method for the Optical Device)

In the optical device shown in FIG. 6, with an increase of the frequencyof the voltage applied to the electrodes 23 and 24 (the frequencythereof being sufficiently higher than a frequency corresponding to theresponse speed of the molecules of the liquid crystal, i.e. thefrequency to which the molecules of the liquid crystal cannot respond,e.g. several Hz to several tens Hz), the voltage reaches a level VA atwhich Frederick transition takes place. At a voltage higher than orequal to VA, the molecules of the liquid crystal begin to be aligned ina perpendicular direction from the orientation in parallel to theelectrode due to the dielectric constant anisotropy of the molecules ofthe liquid crystal. By further increasing the applied voltage, themolecules of the liquid crystal are statistically aligned in aperpendicular direction to the electrode (such given voltage is definedas VT).

Conventionally, since the liquid crystal layer is driven by varying thevoltage between the voltage VT and a voltage lower than or equal to VA(normally OV), the driving speed cannot be increased. In contrast, thedriving method according to this embodiment can drive the liquid crystallayer 22 at an increased speed by applying a voltage higher than orequal to the voltage VT.

When such high voltage is applied, the liquid crystal becomesstatistically unstable to cause electrofluid dynamic motion. Because ofthis, the molecules of the liquid crystal effectively sway between anorientation perpendicular to the electrode and an orientation slightlyinclined from the perpendicular position. Such sway motions are made insynchronism with an interval of an applied voltage including alternatingcurrent. It should be noted that the liquid crystal as a whole has apoor polarizing ability, so that there is a small difference in swayingmotion due to the polarity of the voltage. Therefore, the frequency ofthe motion of the liquid crystal becomes twice the applied voltage.Further, the magnitude of the swaying motion becomes greater inproportion with an increase of the amplitude of the applied voltage.Furthermore, the relaxation time becomes significantly shorter than thestatic relaxation time. Therefore, the refractive index of the liquidcrystal layer 22 can be varied at a frequency twice the applied voltagein synchronism therewith, thus enabling speeding up.

As set forth above, with this embodiment, the optical property (such asa focal length and so forth) can be varied at a high speed periodicallyin synchronism with the applied voltage.

Further, in this embodiment, as set forth above, since electrofluiddynamic motion can be increased by increasing the applied voltage, theeffective response speed can be advantageously increased. Therefore, inthis embodiment, in comparison with the prior art, a higher speedoperation can be achieved.

This driving method will be discussed in detail with reference to thedrawing.

FIG. 30 shows the behavior of the deflection angle when the amplitude ofthe envelope of the voltage is varied between a value that is higherthan or equal to VT and a value that is lower than or equal to VT, e.g.about OV as in the prior art. As one example, as the applied voltage, asine wave having a frequency of 30 Hz was used. The amplitude was variedin a sine-wave-like pattern. In the drawing, the behavior of thedeflection angle due to the variation in the amplitude of the appliedvoltage is illustrated in an-envelop-like representation (i.e. fineperiodic motion of the applied voltage and the deflection angle arerepresented by densely drawn lines).

When the liquid crystal is driven such that the amplitude of theenvelope of the voltage is lower than VT (approximately OV) as in theprior art, there is a problem that in the vicinity of the region wherethe amplitude of the voltage is small, the deflection angle hasasynchronous behavior which is clearly different from the period of theapplied voltage. In the region showing asynchronous behavior, the lightbeam is significantly diverted to make it difficult to definitelydetermine the deflection angle.

On the other hand, FIGS. 31 and 32 show the behavior of the deflectionangle in the case where the envelope of the applied voltage is varied ata voltage amplitude greater than or equal to VT as set forth above. FIG.31 is illustrated in an envelope-like representation as in FIG. 30, andFIG. 32 shows the detailed correspondence between the applied voltageand the deflection angle. Further, the applied voltage was in the formof a sine wave having a frequency of 30 Hz, and its amplitude was variedin a-sine-wave-like pattern.

As is clear from FIG. 32; by varying the amplitude of the voltage at thevoltage higher than or equal to Vt, it can be appreciated that thedeflection angle can be varied at a frequency twice the frequency of theapplied voltage in synchronism with a period of the applied voltage. Inthe region where the voltage is higher than or equal to VT, even astepwise abrupt variation in the amplitude causes no disturbance in thedeflection angle substantially, following the variation of the amplitudein synchronous fashion. Further, from FIG. 31, it is appreciated thatthe magnitude of the periodic variation in the deflection angle isvariable depending upon the amplitude of the applied voltage, and noasynchronous behavior is included. Furthermore, when the amplitude ofthe voltage higher than or equal to VT is varied as discussedpreviously, diverting of the light beam can be constantly suppressed tobe low.

As set forth above, with this embodiment, high-speed response can beachieved.

FIGS. 33 to 37 show other embodiments of this driving method. Thebehavior of an optical property (e.g. deflection angle) of the opticaldevice according to the present invention depending upon the frequencyof the applied voltage (amplitude >VT) will be discussed. It should benoted that, as an example of the applied voltage, a sine wave isemployed. FIGS. 33 to 36 respectively illustrate the behavior of thedeflection angle at the frequencies of the applied voltage of 0.5 Hz, 1Hz, 3 Hz and 100 Hz.

The deflection angle shows a synchronous response even at a lowfrequency, i.e. 0.5 Hz, but the waveform of the deflection angle is notconstant and is disturbed. The variation in the average value in oneperiod is large. Thus, the waveform is disturbed as a whole.Furthermore, in this case, a large light beam diverting is caused. Incontrast, in the case of 1 Hz, the disturbance of each waveform is notso large as in the case of 0.5 Hz, and the variation of the averagevalue in one period becomes smaller. In the case of 3 Hz, thedisturbance becomes further smaller. In addition, in the case of 1 Hzand 3 Hz, diverting of the light beam observed in the case of 0.5 Hz,becomes extremely small. Furthermore, at a further higher frequency,such as 100 Hz, a neat response waveform with quite small disturbanceand scattering can be obtained. Therefore, in order to restrictdisturbance of the deflection angle and scattering of the light beam, itis desirable to set the frequency of the applied voltage to be higherthan or equal to 1 Hz.

FIG. 37 illustrates the behavior of the deflection angle when thefrequency of the applied voltage is varied in a range of 5 Hz to 100 Hz.(It should be noted that, similarly to FIGS. 30 and 31, fine periodicmotion of the applied voltage and the deflection angle is represented bydensely drawn lines). The deflection angle shows a substantially similarmagnitude of variation at the frequency of the applied voltage up toabout 10 Hz. When the frequency becomes higher than 10 Hz, the magnitudeis gradually reduced according to the increase in frequency of theapplied voltage and becomes quite small at a frequency of about 100 Hz.Accordingly, from the viewpoint of ensuring the magnitude of variationin the deflection angle, it is desirable to maintain the frequency ofthe applied voltage to be lower than or equal to 100 Hz. Therefore, thefrequency of the applied voltage according to the present invention ispractical in a range of 1 Hz to 100 Hz.

It should be noted that, although in this embodiment, a sine wave isused as the applied voltage, a similar effect can be produced even inthe case of a rectangular wave, a triangular wave or other periodicwaves.

The above described driving method is applicable to any of the opticaldevices discussed above.

(Three-Dimensional Display Device Employing Optical Device)

A three-dimensional display device employing the aforementioned opticaldevice will now be discussed.

At first, a conventional three-dimensional display device will beexplained. There has been known a conventional three-dimensional displaydevice, employing liquid crystal shutter eyeglasses as shown in FIG. 38.In the device shown in FIG. 38, at first, in order to obtain a so-calledbinocular disparity image by picking up images of a three-dimensionalobject 51 in different directions, the image of the three-dimensionalobject 51 is picked up by two cameras 52 and 53 positioned at apredetermined interval.

Then, two-dimensional images picked up by the respective cameras 52 and53 are synthesized by an image signal conversion device 54 so that thetwo-dimensional images picked up by the cameras 52 and 53 are arrangedalternately per each field.

The image signal conversion device 54 displays the synthesizedtwo-dimensional images on a CRT display device 55, and drives a liquidcrystal shutter on the left side of an observer 57 in liquid crystalshutter eyeglasses 56 to be transparent and the liquid crystal shutteron the right side to be not transparent when the two-dimensional imagepicked up by the camera 52 is displayed.

On the other hand, when the image signal conversion device 54 displaysthe two-dimensional image picked up by the camera 53 on the CRT displaydevice SS, the image signal conversion device 54 drives a liquid crystalshutter on the right side of the observer 57 in the liquid crystalshutter eyeglasses 56 to be transparent and the liquid crystal shutteron the left side to be not transparent.

By repeating the operation set forth above, by the after image effect ofthe eye, the observer 57 feels as if he or she is simultaneously lookingat the binocular disparity images with both eyes, to realize athree-dimensional view by binocular disparity.

There has been known a three-dimensional display device not employingeyeglasses or the like, but a known lenticular lens sheet as shown inFIG. 39.

In this device, similarly to the device employing the liquid crystalshutter eyeglasses, at first, the binocular disparity images of thethree-dimensional object 51 are picked up by the cameras 52 and 53.

Next, respectively the image signal conversion device 54 synthesizes thetwo two-dimensional images picked up by the cameras 52 and 53, to form atwo-dimensional image in which pixels are arranged alternately in ahorizontal direction.

The image signal conversion device 54 displays the synthesizedtwo-dimensional image on a matrix type two-dimensional display device59, typified by a liquid crystal display device.

At this time, the lenticular lens sheet 58 is closely fitted to thescreen of the two-dimensional display device 59. Consequently, since thelenticular lens sheet 58 has directivity, the observer can perceive, byhis left and right eyes only pixels of the two-dimensional images pickedup respectively by the cameras 52 and 53 according to the position ofthe observer 57.

Accordingly, the binocular disparity images picked up at a predeterminedinterval can be seen by both eyes of the observer 57, respectively, tothus form a three-dimensional image by the effect of binoculardisparity.

For example, holography is known, and can be employed to provide athree-dimensional display device capable of forming a more naturalthree-dimensional image.

In holography, interference fringes are picked up when an object lightbeam (a transmitted or reflected light beam produced by irradiating thethree-dimensional object 51 with light from a coherent light source) anda reference light beam radiated from the light source intersect at apredetermined angle.

In the case of reproduction of a three-dimensional image, the picked-upinterference fringe is read out by a light beam having a wavelengthequal to that of the light beam used in picking up, to thus obtain athree-dimensional image of the three-dimensional object 51.

In the conventional three-dimensional display device employing theliquid crystal shutter eyeglasses, it is constantly required to wear theliquid crystal shutter eyeglasses. In the case of communication such astelevision conferences, it becomes difficult to see the faces ofattendants and this gives an give awkward feeling.

In case of the three-dimensional display device employing the lenticularlens sheet, the range where the binocular disparity images can be viewedby both eyes of the observer is quite limited. Therefore, the observercannot freely select the position relative to the two-dimensionaldisplay device 59.

Moreover, since the range to be observed is narrow, a plurality ofpeople cannot observe the range at one time.

Furthermore, in the three-dimensional display device employing theliquid crystal shutter eyeglasses and the three-dimensional displaydevice employing the lenticular lens sheet, the eye of the observer isaccommodated on the screen of the display device, and the accommodationis not varied according to the images to be displayed.

This may cause discrepancy between the convergence perceived by theobserver 57 and the accommodated position of the eye, thus inducingasthenopia.

Further, the two-dimensional image displayed on the display device isfixed at the visual positions which are, in turn, determined by thepositions of the cameras 52 and 53. Therefore, it is not possible toexpress the movement. Even when the observer 57 moves, the imagedisplayed on the display device looks to move together with theobserver. This gives the observer a sense of incompatibility.

In the three-dimensional display device employing holography, a coherentlight beam such as a laser beam is required in picking-up thethree-dimensional object. Further, the information amount to be obtainedbecomes huge to make it impossible to process the information of amoving picture at a real time.

According to the present invention, a three-dimensional display deviceemploying the aforementioned optical device can solve the problemsdescribed above. Consequently, an object of the three-dimensionaldisplay according to the present invention is to satisfy the binoculardisparity, convergence and accommodation and movement parallax as visualcues to depth perception in three-dimensional views without employingeyeglasses or the like, and to achieve moving picture displaying whichcan be re-written electrically.

Further, it is another object of the present invention to provide adriving method for driving the three-dimensional display device whichcan satisfy the binocular disparity, convergence and accommodation andmovement parallax as visual cues to depth perception inthree-dimensional view without employing the eyeglasses or the like, andcan achieve moving picture displaying which can be re-writtenelectrically.

Preferred embodiments of the three-dimensional display device accordingto the present invention will be described hereinafter in detail withreference to the accompanying drawings.

Like molecules or corresponding parts having like functions will bedesignated by the same reference numerals throughout the all figuresillustrating the three-dimensional display device according to thepresent invention.

(First Embodiment of Three-Dimensional Display Device)

FIG. 40 is a block diagram illustrating a schematic construction of thefirst embodiment of a three-dimensional display device according to thepresent invention. In FIG. 40, reference numeral 61 denotes atwo-dimensional display device; 62, a varifocal lens; 63, a drivingdevice; 64, a synchronization device; 65, a three-dimensional image; 66,an observer; and 67, a two-dimensional image.

In FIG. 40, the two-dimensional display device 61 is well known as a CRT(Cathode Ray Tube), a liquid crystal display, an LED display, plasmadisplay, a projector type display, a vector-scanning type display or thelike. The varifocal lens 62 is the optical device as set forth above.

The two-dimensional display device 61 is arranged inside of the focallength of the varifocal lens 62, namely at the position closer to thevarifocal lens 62 than the focal length.

The varifocal lens 62 is interposed between the two-dimensional displaydevice 61 and the observer 66, to vary the focal length at apredetermined speed according to an output from the driving device 63,described later.

The driving device 63 is a known signal generator having a predeterminedduty ratio and a predetermined period and outputting driving signals offrequencies f12 and f22 having the same amplitude.

Although this embodiment employs the driving signals of frequencies f12and 22 having the same amplitude as outputs from the driving device 63,it is may employ signals of frequencies having various amplitudes.

The synchronization device 64 is adapted to synchronize the focalposition of the varifocal lens 62 and the two-dimensional imagedisplayed on the two-dimensional display device 61. For example, thesynchronization device 64 generates a synchronization signal after alapse of a delay period until the focal length of the varifocal lens 62is varied on the basis from the output from the driving device.

The three-dimensional image 65 is used for explaining the image to beviewed by the observer 66 in the case where the first embodiment of thethree-dimensional display device is employed. In this embodiment, theimage is displayed as a virtual image.

Eyes of the observer 66 represents a view position of the observer 66.The two-dimensional image 67 represents an image to be displayed on thetwo-dimensional display device 61, which is generated by decomposing thethree-dimensional image into the two-dimensional image represented on aplane at predetermined intervals according to procedures describedlater. Namely, the two-dimensional image 67 are a depth sampled image.

FIG. 41 graphically shows a state of variation of the focal length whenthe varifocal lens is driven by the driving device in the firstembodiment. In FIG. 41, the horizontal axis represents a driving timeand the vertical axis represents a focal length.

It should be noted that the waveform of the driving signal isrectangular, as shown in FIG. 813, in which a low frequency f21 (Δ∈>0)and a high frequency f22 (Δ∈1<0) are used. The refractive index of thedual-frequency liquid crystal (variable refractive index material)becomes smaller than the refractive index of the transparent materialwhen the dual-frequency liquid crystal is erected perpendicularly to thetransparent electrodes 23 and 24. On the other hand, when thedual-frequency liquid crystal is disposed substantially in parallel tothe transparent electrodes 23 and 24, the refractive index of thedual-frequency liquid crystal becomes greater than that of thetransparent material.

As a result, it is obvious from FIG. 41 that the focal length of thevarifocal lens 12 is varied in an analogous sequential manner. Therepetition frequency of the low frequency f12 and the high frequency f22is substantially 30 Hz.

Accordingly, remarkably high speed operation can be achieved, byemploying the varifocal lens in the above-described optical device, incomparison with the conventional liquid crystal lens which takes severalseconds for resumption.

The operation of the first embodiment of the three-dimensional displaydevice will be discussed with reference to FIGS. 42A and 42B.

FIG. 42A is an illustration for explaining operation of thethree-dimensional display device, and FIG. 42B is an illustration forexplaining the two-dimensional image to be displayed on thetwo-dimensional display device 61.

In FIGS. 42A and 42B, a virtual image 68 is a two-dimensional imageformed at a position 69, and a virtual image 110 is atwo-dimensional-image formed at a position 111. Reference symbol d_(obj)designates a distance between the varifocal lens and the two-dimensionaldisplay device; and d_(img), a distance between the varifocal lens andthe imaging point of the virtual image. FIG. 42B shows athree-dimensional image 112 and an aggregate 113 of the two-dimensionalimages.

It should be noted that the reason why the minus (−) sign is given tothe distance dung between the varifocal lens and the imaging point ofthe virtual image is that the direction toward the observer 66 from thevarifocal lens 62 is taken to be plus (+).

Next, discussion will be given on operation of the first embodiment ofthe three-dimensional display device in reference to FIGS. 40, 42A and42B. As described above, the position (view position) of thetwo-dimensional display device is set at a position where the d_(obj) issmaller than the focal length of the varifocal lens 62. Therefore, thetwo-dimensional image 67 displayed on the two-dimensional display device61 is observed as a virtual image by the observer 66.

At this time, conforming to the equation (1) below according to aparaxial theory as a theory of optics of the lens, the imaging point 69of the virtual image 68 of the two-dimensional image 67 can be varied inthe depth direction toward the imaging point 111 of the virtual image110 by varying the focal length of the varifocal lens 62.1/d _(obj)+1/d _(img)=1/f _(o)  (1)

wherein f_(o) is a focal length of the varifocal lens 62.

As shown in FIG. 42B, for example, the three-dimensional image 112 isexpressed as an aggregate of the two-dimensional images sampled towardthe depth direction from the visual direction when the three-dimensionalimage 112 is picked up or displayed, and the respective two-dimensionalimages are displayed on the two-dimensional display device 61 in a timedivision manner.

At this time, synchronization of the two-dimensional display device 61and variation of the focal length of the varifocal lens 62 isestablished by the synchronization device 64 so that the imaging pointof the two-dimensional image to be displayed on the two-dimensionaldisplay device 61 accords with the sampling position in the depthdirection. Consequently, due to an after image effect of the eyes of theobserver 66, the three-dimensional image 65 to be displayed on thetwo-dimensional display device 61 can be observed as an aggregate(virtual image) of the images sampled in the depth direction viewed fromthe observer 66.

As described above, in the first embodiment of the three-dimensionaldisplay device, an image obtained by sampling the three-dimensionalimage 112 into two-dimensional images represented on the two-dimensionalplane at predetermined intervals is displayed on the two-dimensionaldisplay device 61. The two-dimensional images to be displayed on thetwo-dimensional display 61 are displayed at the same positions as thoseat the time of sampling based on an output from the synchronizationdevice 64 for generating a signal in synchronism with variation in focallength of the varifocal lens 62. Thus, on the basis of the foregoingequation (1), the imaging point of the two-dimensional image (virtualimage) to be displayed on the two-dimensional display device 61 can bevaried so that the three-dimensional image 112 can be displayed as thevirtual image 65, i.e., an aggregate of the sampled images in the depthdirection.

In the first embodiment of the three-dimensional display device, sincethe observer 66 views the three-dimensional image 65 as the aggregate ofthe virtual images substantially aligned in the depth direction. Thus,visual cues to depth perception in three-dimensional view such asbinocular disparity, convergence, accommodation and movement parallaxcan be satisfied without causing any discrepancy, and a naturalthree-dimensional image can be realized.

Moreover, in the first embodiment of the three-dimensional displaydevice, an amount of information necessary for displaying is determinedaccording to the number of samples in the depth direction. Resolution inthe visual direction (depth direction) of the human being is known to belower than resolution in the vertical and horizontal directions.Therefore, the number of the samples in the depth direction can becomegreatly smaller than that required in the vertical and horizontaldirections. According to the present invention, the information amountrequired for displaying can be remarkably reduced in comparison with theholography.

Additionally, since the information amount can be remarkably reduced,the three-dimensional display device in the first embodiment can beapplicable to the case of displaying, e.g., a moving picture, which mustbe displayed at high speed.

Furthermore, since the three-dimensional display device in the firstembodiment utilizes the normal lens effect by the varifocal lens 62, acoherent light source such as a laser beam source is not required as thelight beam source. Furthermore, since an influence of difference ofcolors in the two-dimensional image 67 is slight, it is easy to achievecolor image display.

Furthermore, since no mechanical driving portion is required, thethree-dimensional display device in the first embodiment is advantageousin reduction of a weight and improvement of reliability.

Although in this embodiment two frequencies are used, the number offrequencies should not be limited to two, and the greater number offrequencies may be employed.

(Second Embodiment of Three-Dimensional Display Device)

FIG. 43 is a view showing a schematic construction of athree-dimensional display device in the second embodiment according tothe present invention. In the second embodiment shown in FIG. 43, thebasic construction is the same as that of the three-dimensional displaydevice in the first embodiment, and different from the first embodimentin that the two-dimensional display device 61 is arranged outside of thefocal length as viewed from the varifocal lens 62, and that thethree-dimensional image 112, i.e., the aggregate 113 of the twodimensional images is displayed on the two-dimensional display device 61in a manner invented in the vertical and horizontal directions.

As obvious from FIG. 43, since the two-dimensional display device 61 isarranged outside of the varifocal length as viewed from the varifocallens 62 in the three-dimensional display device in this secondembodiment, the observer 66 may view the three-dimensional image (realimage) formed between the varifocal lens 62 and the observer 66.

FIG. 44 is an illustration for explaining operation of the secondembodiment of the three-dimensional display device. Hereinafter,description will be given on operation of the second embodiment of thethree-dimensional display device with reference to FIG. 44.

In FIG. 44, the real image 116 is a two-dimensional image formed at animaging point 117, and another real image 114 is a two-dimensional imageformed at another imaging point 115.

At first, as shown in FIG. 44, the imaging point 115 of the real image114 of the two-dimensional image 67 can be varied in the depth directionfrom the observer 66 toward the imaging point 117 of the real image 116by varying the focal length of the varifocal lens 62.

Accordingly, similarly to the first embodiment as set forth above, thethree-dimensional image is expressed as the aggregate 113 of thetwo-dimensional images sampled in the depth direction, and therespective two-dimensional images in the aggregate 113 are displayed onthe two-dimensional display device 61 in a time division manner.Further, the focal lengths of the two-dimensional display device 61 andvarifocal lens 62 are synchronized by the synchronization device 64 sothat the imaging points of the respective two-dimensional images accordwith the sampling position in the depth direction. Thus, utilizing theafter image effect of the human eyes, the three-dimensional image can bereproduced as an aggregate of the sampled images (real image) in thedepth direction.

Accordingly, this embodiment of the three-dimensional display deviceachieves the same advantageous result as that of the first embodiment ofthe three-dimensional display device. In addition, since the secondembodiment of the three-dimensional display device can form the realimage, it becomes possible to pick up the two-dimensional image byplacing a beaded plate at the imaging point.

Otherwise, by placing a scattering plate at the imaging point, only thetwo-dimensional image at that position can be viewed.

(Third Embodiment of Three-Dimensional Display Device)

FIG. 45 is a block diagram illustrating a schematic construction of athird embodiment of the three-dimensional display device according tothe present invention. Reference numeral 151 denotes a projection typedisplay; 152, a shutter; 153, a scattering plate; 154, an imagerecording and reproducing apparatus; and 155, a synchronization controldevice.

In FIG. 45, the projection type display 151 has been well known. In thethird embodiment, a plurality of displays are employed for lowering adepiction speed of the respective projection type displays.

The shutters 152 are provided in the respective projection type displays151, for projecting images from each of projection type displays 151 onthe scattering plate 153 in a time division manner.

The scattering plate 153 is of a known type for displaying the imageprojected from the projection type display 151. For example, thescattering plate 152 is placed within the focal length of the varifocallens 62, similarly to the first embodiment.

The image recording and reproducing apparatus 154 is of a known type,such as a video recorder. The image recording and reproducing apparatus154 outputs an image signal to the projection type display 151 connectedthereto on the basis of the output from the synchronization controldevice 155.

The synchronization control device 155 controls operation of the imagerecording and reproducing apparatus so that the image signal can beoutput in synchronism with variation in the focal length of thevarifocal lens 157 on the basis of the output from the driving device63. Further, the synchronization control device 155 controls therespective shutters 152, for projecting the image of the selected one ofthe projection type display 151 onto the scattering plate 153.

Next, the operation of the third embodiment of the three-dimensionaldisplay device according to the present invention will be discussed withreference to FIG. 45. Similarly to the foregoing first embodiment, thethree-dimensional image 112 shown in FIG. 42B is expressed as theaggregate 113 of the two-dimensional images sampled in the depthdirection. These two-dimensional images are projected in order from theprojection type display 151 and displayed in order on the scatteringplate 153 in a time division manner by the respective shutters 152.Simultaneously, the image recording and reproducing apparatus 154 andthe focal length of the varifocal lens 62 are synchronized such that theimaging point of each two-dimensional image accords with the samplingposition. Consequently, the three-dimensional image can be reproduced asan aggregate of the sampled images (virtual images) utilizing the afterimage effect of the human eyes.

Thus, the same advantageous result can be produced as that of thethree-dimensional display devices in the foregoing embodiments.Additionally, a screen size can be increased easily since the projectiontype display 151, shutter 152 and scattering plate 153, which all havebeen known.

It should be noted that, in the third embodiment of thethree-dimensional display device, it is possible to place the scatteringplate 153 and the varifocal lens 157 in a positional relationshipsimilar to the second embodiment in which the scattering plate 153 isplaced outside of the focal length of the varifocal lens 157 so as toachieve three-dimensional displaying by projecting vertically andhorizontally invented images (two-dimensional images) from the imagerecording and reproducing apparatus 154.

FIG. 46 is view showing another schematic construction of the varifocallens to be used in the three-dimensional display device. Referencenumerals 161 and 162 denotes transparent electrodes; 163, a variablerefractive index material; and 164, an aperture.

In FIG. 46, the transparent electrodes 161 and 162 has been known andare formed of an ITO film, a ZnOx film or the like. The aperture 164 isformed on the transparent electrode 161, as shown in FIG. 46.

The variable refractive index material 163 is formed of a polymerdispersed liquid crystal, a polymer liquid crystal or the like, and itsrefractive index is varied depending upon a voltage applied to thetransparent electrodes 161 and 162.

It should be noted that in the varifocal lens in the third embodiment ofthe three-dimensional display device, the configuration of the aperture164 formed on the transparent electrode 161 is circular. However, theshape of the aperture is not limited to be circular, and can be variablewith respect to the direction of the light beam. For instance, theaperture may be formed into a strip if the focal length is varied onlyin one direction.

Although the present invention made by the inventors has been describedin detail and particularly in the preferred embodiments, the presentinvention should not be limited to these embodiments, but can bemodified in various ways without departing from the spirit and the scopeof the invention.

For example, it is also possible to reproduce a three-dimensional image172 by employing a line depiction device 171 (such as a laser scanningdepiction device or an electron beam scanning depiction device) as atwo-dimensional display device to express the three-dimensional image172 as an aggregate of lines or dots in place of the sampled images inthe depth direction, and by varying the focal length of the varifocallens 62 in accordance with the position of the lines or dot in the depthdirection by employing the synchronization device 64, as shown in FIG.47.

This system is applicable to the foregoing embodiments. This system canproduce the same advantageous results as those achieved by the foregoingembodiments. Furthermore, since this system can reduce the number ofcomponents required for achieving the three-dimensional display, thusfacilitating analogous (sequential) display in the depth direction.

According to the present invention, the three-dimensional image isdisplayed by varying the focal length of the varifocal lens 62 so as tovary the imaging point of the image (virtual image or real image)displayed on the two-dimensional display device 171 in the depthdirection. Since the resolution in the depth direction of the humanbeing is markedly low at the far position in comparison with that in thenear position, it may be possible to reduce the overall informationamount by increasing the number of samples at the near position to theobserver 66 and reducing the number of samples farther from the observer66.

As illustrated in FIG. 48, it can be considered that the motion speed ofthe image by the varifocal lens is not constant in the depth direction.

In this case, if the brightness of the two-dimensional images areconstant, the image where the motion speed is low appears brighter andthe image where the motion speed is high appears darker to make thebrightness as viewed by the observer non-uniform.

Therefore, it is quite useful to vary the brightness of thetwo-dimensional image according to the motion speed of the varifocallens.

As illustrated in FIG. 48, the focal length of the varifocal lens isvaried periodically between the position near to the eyes and theposition far from the eyes.

In such driving manner driving, there are two cases: (1) from the nearposition to the far position; and (2) from the far position to the nearposition. These two motions are reverse in direction, but pass throughthe same depth positions.

Accordingly, by depicting different images in the cases of (1) and (2),the three-dimensional display device of the present invention can bedriven more efficiently.

(Fourth Embodiment of Three-Dimensional Display Device)

With the three-dimensional display devices in the foregoing embodiments,since the two-dimensional images sampled in the depth direction aredisplayed in time division to be thus integrated into thethree-dimensional image by an after image effect, it is impossible toavoid a phantom phenomenon, which allows the back side or inside of theobject which should be hidden from the observer's sight to be viewedtransparently. This is an immense obstacle to reproduction of thenatural three-dimensional image, and is the reason why thethree-dimensional display devices in the foregoing embodiments are usedonly for reproducing wire frame like images. Hereinafter, athree-dimensional display device capable of avoiding the above-stateddrawback will be described with reference to FIGS. 49 to 59.

FIG. 49 is a schematic view showing a construction of the fourthembodiment of the three-dimensional display device according to theinvention, and FIG. 50 is an illustration for explaining basic operationof the fourth embodiment of the three-dimensional display device foravoiding the phantom phenomenon.

In FIGS. 49 and 50, reference numeral 201 denotes a phantomthree-dimensional display device; 202, a shutter device; 202A, a shutterelement of the shutter device 202; 203, a phantom image (real image);204, eyes of an observer; 205, a transmitted light beam; 206, a blockedlight beam; 207, a portion where blocking, scattering and reflectingfunctions are effected.

The fourth embodiment uses an example in which a three-dimensional imageis reproduced as a real image outside of the phantom three-dimensionaldisplay device. The term “Phantom” refers to a phenomenon which allowsthe back side or inside of an object which should be hidden to be viewedtransparently.

As shown in FIG. 49, the fourth embodiment of the three-dimensionaldisplay device comprises the phantom three-dimensional display device201 and the shutter device 202 arranged at a position including thephantom three-dimensional image 203.

The phantom three-dimensional display device 201 is exemplified in avarifocal three-dimensional display device or a depth direction samplingtype device such as a varifocal mirror type device, a varifocal lenstype device, an oscillation screen type device, a display area layertype device or a rotary type device. The phantom three-dimensionaldisplay device 201 reproduces the phantom image 203 by, for example,displaying images sampled in the depth direction in a time divisionmanner. This phantom image is practically displayed with development inthe depth direction. Therefore, although it becomes possible to satisfyvisual cues to depth perception in the three-dimensional view, such asbinocular disparity, convergence, accommodation and movement parallaxwithout any discrepancy, there arises a problem that the back side orinside to be hidden is viewed transparently. Namely, normally, a lightbeam is scattered/reflected on the surface of a generalthree-dimensional object, and simultaneously, a light beam from the backside is blocked. However, the phantom three-dimensional display devicecan only express the former function. The three-dimensional displaydevice as shown in FIG. 43 is one example of the phantomthree-dimensional display device.

The shutter device 202 is a device including a guest-host liquidcrystal, a polymer dispersed liquid crystal, a holographic polymerdispersed liquid crystal or the like; or a device including a photoreactive element in which the state of an imaging point is turned into alight blocking state, a light scattering state or a light reflectingstate by converged light at the imaging point of a real image.

Next, the basic operation of the fourth embodiment of thethree-dimensional display device for avoiding the phantom phenomenonwill be, discussed with reference to FIG. 50.

As shown in FIG. 50, the fourth embodiment of the three-dimensionaldisplay device is constructed by arranging the shutter elements 202Aforming the shutter device 202, for example, in the vicinity of thesampling positions in the depth direction (for simplicity ofillustration, only one is shown in the drawing). At the positioncorresponding to the image sampled in the depth direction in thevicinity of the shutter element during a period when the phantomthree-dimensional image 203 behind of the shutter element 202A (asviewed from the eyes 204 of the observer) is reproduced, the function toblock, scatter or reflect the light beam is made effective formaintaining a transparent condition at other positions for otherperiods. Thus, the light beam coming from behind of the shutter element(as viewed from the eyes 204 of the observer) can be blocked orattenuated. This means that the frontal portion of the object blocks thelight beam from the back portion, and the condition where the backsideof the object cannot be seen can be simulated.

Accordingly, the phantom portion of the phantom three-dimensional image203 can be made invisible by arranging the shutter elements 202A in thevicinity of the necessary sampling position in the depth direction.Therefore, it is possible to obtain a natural three-dimensionalreproduced image without any phantom image.

Since the images sampled in the depth direction to be supplied to thephantom three-dimensional display device 201 can be also used asinformation to the shutter device 202, an information amount requiredfor displaying the three-dimensional image excluding the phantom imageis equal to that required for phantom three-dimensional display device201, thus preventing any increase in information amount.

Furthermore, the information amount is mainly determined by the numberof images sampled in the depth direction. Here, it has been known thatthe resolution of the human being in the depth direction is lower thanthat in the vertical and horizontal direction. Therefore, the number ofimages sampled in the depth direction can be remarkably reduced incomparison with that in the vertical and horizontal direction.

Accordingly, the fourth embodiment is advantageous in that the requiredinformation amount can be markedly reduced in comparison with thatrequired for holography and so forth. Therefore, the three-dimensionaldisplay device in the fourth embodiment can be satisfactorily applied tothe case where, for example, a moving picture must be displayed at ahigh speed.

Moreover, since the fourth embodiment requires only addition of theshutter device 202, an influence by a color difference of the displayedimage can be reduced to facilitate displaying in color. Further, sincethe fourth embodiment does not include mechanical driving portions, itis suitable for reduction of a weight and improvement of reliability.

Although the fourth embodiment uses an example in which most of thelight beam from the backside is blocked by the shutter device 202, alight blocking ratio of the shutter device 202 can be set to a desiredvalue so as to easily express a semi-transparent or transparentthree-dimensional object (such as glass or transparent plastic).

(Fifth Embodiment of Three-Dimensional Display Device)

The fourth embodiment as set forth above uses one example according tothe present invention, in which the three-dimensional image is a realimage. It is also possible to avoid the phantom phenomenon even if thethree-dimensional image is a virtual image. In the fifth embodiment, adescription will be given on a varifocal lens type device as a phantomthree-dimensional display device in which a phantom three-dimensionalimage is reproduced as a virtual image. The fifth embodiment of thethree-dimensional display device will be discussed hereinafter withreference to FIGS. 51 and 52.

FIG. 51 is a view showing a schematic construction of the fifthembodiment of the three-dimensional display device according to thepresent invention, and FIG. 52 is an illustration for explaining basicoperation of the fifth embodiment of the three-dimensional displaydevice for avoiding a phantom phenomenon.

In FIGS. 51 and 52, reference numeral 202 denotes a shutter device; 202Aa shutter element of the shutter device 202; 204, the eyes of anobserver; 205, a transmitted light beam; 206, the blocked light beam;207, a portion where blocking, scattering and reflecting functions areeffected; 208, a two-dimensional display device; 209, the varifocallens; 210, a phantom three-dimensional image (virtual image); and 211, avirtual image of the shutter element 202A.

As shown in FIG. 51, the fifth embodiment of the three-dimensionaldisplay device comprises the two-dimensional display device 208, avarifocal lens type phantom three-dimensional display device constructedof the varifocal lens 209, and the shutter device 202 interposed betweenthe varifocal lens 209 and the two-dimensional display device 208.

The two-dimensional display device 208 is, for example, a CRT, a liquidcrystal display, an LED display, a plasma display, a projection typedisplay, a line depiction type display and the like. For example, alaser scan depiction device, a CRT (electron beam scan depiction device)and the like can be employed.

The varifocal lens 209 comprises a fixed focus lens, a variablerefractive index material, and electrodes sandwiching the lens and thematerial there between.

Here, the two-dimensional display device 208 is arranged within thefocal length of the varifocal lens 209. Therefore, the image to beviewed becomes a virtual image.

The phantom three-dimensional display device reproduces the virtualimage by displaying the sampled images in the depth direction in a timedivision manner, for example. The phantom three-dimensional displaydevice uses an example shown in FIG. 40.

Next, the basic operation for avoiding the phantom phenomenon in thefifth embodiment of the three-dimensional display device will bediscussed with reference to FIG. 52.

Unlike the fourth embodiment, in the fifth embodiment, it is meaninglessto place the shutter device 202 at the virtual image position since thefunctions of blocking, scattering and reflecting of the light beamcannot be effected. The light beams are actually converged at the realimaging point. In contrast, the light beams look like coming from thevirtual image, and are not converged actually.

Therefore, the shutter elements 202A (only one is shown forsimplification of illustration) of the shutter device 202 is placed at aposition between the two-dimensional display device 208 and thevarifocal lens 209, which position is optically equivalent to thevirtual image position and the light beam actually passes. By thisarrangement, the shutter device 202 is also projected at the virtualimage position by the effect of the varifocal lens 209. Thus, it ispossible to produce the same advantageous result as that of the fourthembodiment.

Namely, at the position corresponding to the sample images in the depthdirection during a period when the phantom three-dimensional image 210behind the virtual image (211) of the shutter elements 202A (as viewedfrom the observer 204) is reproduced, the function for blocking,scattering or reflecting the light beam is made effective, and atransparent condition is maintained at other timings and otherpositions. Thus, the light beam coming from behind of the shutterelement 202A (as viewed from the observer 204) is blocked or attenuatedfor the observer. This means that the front portion of the object blocksthe light beam from the rear portion, and the condition where thebackside of the object is invisible, can be simulated.

Accordingly, by this embodiment, similarly to the fourth embodiment eventhe pseudo of phantom three-dimensional image 210, the phantom portioncan be made invisible. Thus, it is possible to obtain a naturalthree-dimensional reproduced image excluding any phantom image.

(Sixth Embodiment of Three-Dimensional Display Device)

In the foregoing fifth embodiment, the shutter device is arranged at aposition which is optically equivalent to the phantom three-dimensionalimage of the virtual image and in which the light beam actually passes.The advantageous result of the present invention can be achieved byarranging the shutter device at a position which is optically equivalentto the phantom three-dimensional image of the image and in which thelight beam actually passes, irrespective of a real image or a virtualimage of the phantom three-dimensional image.

The sixth embodiment uses an example in which a varifocal lens typedevice is employed as the phantom three-dimensional display device andthe phantom three-dimensional image is reproduced as a real image.Discussion will be given on the sixth embodiment of thethree-dimensional display device with reference to FIGS. 53 and 54.

FIG. 53 is a view showing a schematic construction of the sixthembodiment of the three-dimensional display device, and FIG. 54 is anillustration for explaining the basic operation for avoiding a phantomphenomenon in the sixth embodiment of the three-dimensional displaydevice.

In FIGS. 53 and 54, reference numeral 202 denotes a shutter device;202A, a shutter element of the shutter device 202; 203, a phantomthree-dimensional image (real image); 204, an observer; 205, atransmitted light beam; 206, a blocked light beam; 207, a portion whereblocking, scattering and reflecting functions are effected; 208, atwo-dimensional display device; and 209, a varifocal lens.

Like the fifth embodiment, the sixth embodiment of the three-dimensionaldisplay device comprises the varifocal lens type phantomthree-dimensional display device including the two-dimensional displaydevice 208 and the varifocal lens 209, and the shutter device 202interposed between the two-dimensional display device 208 and thevarifocal lens 209, as shown in FIG. 53. Here, the two-dimensionaldisplay device 208 and the varifocal lens 209 are arranged outside ofthe focal length of the varifocal lens 209 so that an image to be viewedbecomes a real image, i.e., a phantom three-dimensional image 203.

Although like the fifth embodiment, the shutter device 202 may bearranged at a position of the phantom three-dimensional image 203, itcan be arranged at a position which is optically equivalent to thephantom three-dimensional image of the virtual image and in which thelight beam actually passes, as shown in FIGS. 53 and 54 (only one isshown for simplification of illustration). With this arrangement, theshutter device 202 is also projected on the real image position by theeffect of the varifocal lens 209. Thus, it is possible to produce thesame advantageous result as that of the fourth embodiment.

Namely, at the position corresponding to the sample images in the depthdirection, during a period when the phantom three-dimensional image 203behind the position of the real image of the shutter elements 202A (asviewed from the observer 204) is reproduced, the function for blocking,scattering or reflecting the light beam is made effective, and atransparent condition is maintained at other timings and otherpositions. Thus, the light beam coming from behind of the shutterelement 202A (as viewed from the observer 204) is blocked or attenuatedfor the observer. This means that the front portion of the object blocksthe light beam from the rear portion, and the condition where thebackside of the object is invisible can be simulated.

Thus, in the sixth embodiment, the advantageous result of the presentinvention can be achieved by arranging the shutter device at theposition which is optically equivalent to the phantom three-dimensionalimage of the virtual image and in which the light beam actually passes,and the natural three-dimensional image without any phantom image can beobtained.

For example, by the use of the depth sample type phantomthree-dimensional display device, when a part of the display devicemoves to the phantom image position, it is physically difficult toarrange the shutter device 202 at that position. Therefore, it may bepossible to optically shift the position of the phantomthree-dimensional image by employing an optical system such as a lens ora mirror, and to arrange the shutter device 202 at the shifted position,as shown in FIG. 55, for example. Even in this case, it is obvious fromthe sixth embodiment that the advantageous result of the presentinvention can be sufficiently achieved.

In this embodiment, like the three-dimensional image 203 shown in FIG.53, a region where the three-dimensional image 203 is reproduced can beset in a space where no object such as the device exists, therebyoffering an advantage of reducing a frame canceling and the like. Here,the frame canceling means a phenomenon that if an object exists withinthe region where the three-dimensional image is reproduced, theconfiguration and the like of the object may influence on therecognition process of a three-dimensional image by the human being suchthat the position of the three-dimensional image is shifted by theinfluence of presence of the object, or the three-dimensional imagesticks on the object to be viewed as the two-dimensional image; or theobserver feels a strange feeling that the three-dimensional image movesin the opposite direction, when he moves his head. Further, in thisembodiment, since the region where the three-dimensional image 203 isreproduced is a mere space, it is possible to advantageously arrange anobject over, under or beside the three-dimensional image so as to reducethe frame canceling.

(Embodiment of Shutter Device to be Employed in Fourth to SixthEmbodiments)

An embodiment of the shutter device to be employed in the presentinvention will be illustrated in FIGS. 56A to 58.

One example of the guest-host liquid crystal element to be employed inthe shutter device is shown in FIGS. 56A and 56B. In FIG. 56A, referencenumeral 321 denotes a guest-host liquid crystal layer; 321A, a liquidcrystal; 321B, a dichroic dye; 322 and 323, alignment layers; 324 and325, electrodes; 326, a power source (applied voltage); and 327, a powerswitch.

As shown in FIG. 56A, the guest-host liquid crystal element comprisesthe guest-host liquid crystal layer 321 composed of a mixture of thedichroic dye (e.g., anthraquinone type dichroic dye or azo type dichroicdye), the liquid crystal (e.g., nematic liquid crystal), the alignmentlayers 322 and 323 and the electrodes 324 and 325 sandwiching theguest-host liquid crystal.

When no voltage is applied between the electrodes 324 and 325, theliquid crystal 321A is aligned in parallel to the alignment layers 322and 323 by anchoring force of the alignment layer 322 and 323.Accordingly, the dichroic dye 321B is also aligned in parallel to thealignment layers, to become, e.g., black and absorb the light beam.Therefore, the light beam coming from the backside is absorbed by thedye so that the intensity of the light beam to be transmitted forwardcan be reduced remarkably.

As shown in FIG. 56B, when a voltage higher than or equal to a thresholdvoltage of the liquid crystal 321A is applied between the electrodes 324and 325, the liquid crystal 321A is aligned perpendicularly to thealignment layers due to its own dielectric constant anisotropy.Accordingly, the dichroic dye 321B is also aligned perpendicularly tothe alignment layers, to thus become transparent, for example. Thus, inthis guest-host liquid crystal element, transmitting and blocking of thelight beam can be switched by the voltage, and therefore, the shutterfunction required in the present invention can be realized.

Since the present invention required only to transmit and block thelight beam by the voltage, a similar effect can be produced by a polymerdispersed guest-host liquid crystal element, in which the guest-hostliquid crystal is dropwise dispersed in the polymer.

FIG. 57 shows one embodiment of the polymer dispersed liquid crystalelement to be employed in the shutter device. The polymer dispersedliquid crystal element comprises a polymer dispersed liquid crystallayer 328, in which the liquid crystal (e.g., nematic liquid crystal)droplets 328B are dispersed in a transparent polymer (e.g., acryl typepolymer) 328A, and electrodes 324 and 325 sandwiching the layer 328.

When no voltage is applied between the electrodes 324 and 325, theliquid crystal droplets 328A are oriented randomly by the anchoringforce of alignment of the polymer around the droplets 328B so that thelight beam is scattered by birefringence of the liquid crystal droplets328B. Therefore, the light beam coming from the backside is scattered bythe polymer dispersed liquid crystal, and then, its intensity isreduced. Next, when a sufficient voltage is applied between theelectrodes 324 and 325, the liquid crystal is aligned perpendicularly tothe electrodes 324 and 325 due to its own dielectric constant anisotropyso that its refractive index becomes substantially equal to that of thepolymer 328A thus to become transparent. Thus, in this polymer dispersedliquid crystal element, transmitting and scattering of the light beamcan be switched by the voltage. Therefore, the shutter function requiredin the present invention can be realized.

Since the present invention requires only to control transmitting andscattering of the light beam by the voltage, the similar effect may beproduced by employing a polymer dispersed liquid crystal, in which thepolymer is dispersed within the liquid crystal in a network fashion.

FIG. 58 shows one embodiment of a holographic polymer dispersed liquidcrystal element to be employed in the shutter device. The holographicpolymer dispersed liquid crystal element comprises a holographic polymerdispersed liquid crystal layer 329, in which the liquid crystal (e.g.,nematic liquid crystal) droplets 328B are dispersed in a laminatedmanner in the transparent polymer (e.g., acryl type polymer) 328A, asshown in FIG. 58, and the electrodes 324 and 325 sandwiching the layer329.

When no voltage is applied between the electrodes 324 and 325, theliquid crystal droplets 328A are oriented randomly by the anchoringforce of alignment of the polymer around the droplets 328B so that thelight beam is scattered by birefringence of the liquid crystal droplets3288, and reflected by Bragg reflection of mufti-layer structure of thepolymer layer 328A and the layer of the liquid crystal droplets 328B.Therefore, the light beam coming from the backside is refracted to,e.g., the back side by the holographic polymer dispersed liquid crystalelement 329, and the intensity of the light beam transmitted forward ismarkedly reduced.

Next, when a sufficient voltage is applied between the electrodes 324and 325, the liquid crystal is aligned perpendicularly to the electrodes324 and 325 due to its own dielectric constant anisotropy so that itsrefractive index becomes substantially equal to that of the polymer 328Ato thus become transparent.

Thus, in this polymer dispersed liquid crystal element, transmission andreflection of the light beam can be switched by the voltage. Therefore,the shutter function required in the present invention can be realized.Here, it is important for the present invention to attenuate the lightbeam intensity to the observer at the front side. Therefore, in thiselement, it is not essential to cause mirror surface reflection, butreflection containing scattering factor or deflection to a region wherethe observer is not present may be sufficiently satisfactory. It is alsoclear that the light intensity to the observer can be reduced owing to achange in Bragg reflection angle by varying an angle of the multi-layerstructure of the layer 328A polymer and the liquid crystal dropletslayer 328B in the holographic high polymer dispersed liquid crystalelement 329.

It is also clearly effective to employ the guest-host liquid crystalshown in FIG. 56A as the liquid crystal portion of the high polymerdispersed liquid crystal and the holographic polymer dispersed liquidcrystal respectively shown in FIGS. 57 and 58.

(Seventh Embodiment of Three-Dimensional Display Device)

The seventh embodiment of the three-dimensional display device issubstantially constructed similarly to the foregoing fourth embodimentshown in FIG. 49, and comprises the phantom three-dimensional displaydevice for reproducing the real image of the phantom three-dimensionalimage 203 and the shutter device 202 arranged at the positions includingthe phantom three-dimensional image 203. Here, the shutter device 202includes a light beam reactive element (e.g., a photochromic material, amaterial causing a photostructural change and a material containing aliquid crystal, or an element containing a liquid crystal in whichnematic-isotropic phase transition temperature is varied by aphotostructural change), in which a converged light beam at an imagingpoint of a real image brings the imaging point into a beam shuttering,scattering or reflecting state.

FIG. 59 is an illustration showing the basic operation of the seventhembodiment of the three-dimensional display device. As shown in FIG. 59,a phantom three-dimensional display device 201 reproduces the phantomthree-dimensional image 203 of the real image by displaying depth sampleimages in a time division manner. The shutter elements 202A forming theshutter device 202 are arranged at the positions including the phantomthree-dimensional image 203. When the three-dimensional image isreproduced from the front side as viewed from the observer, once thephantom image is reproduced (left of FIG. 59), at the imaging point ofthe real image in the shutter device 202, the point is brought into alight beam blocking, light beam scattering or light beam reflectingstate by the action of the light beam reactive element (right in FIG.59). By this, for a predetermined period when the phantomthree-dimensional image 203 of the backside (as viewed from theobserver) portion is reproduced, the light beam coming from the phantomthree-dimensional image of the backside (as viewed from the eyes 204 ofthe observer) is blocked or attenuated. This is equivalent to the factthat the front portion of the object blocks the light beam from the rearportion. Further, the condition where the backside of the object isinvisible can be successfully simulated.

Accordingly, the seventh embodiment of the three-dimensional displaydevice can make the phantom portion invisible so as to obtain thenatural three-dimensional image without any phantom image.

In the seventh embodiment of the three-dimensional display device, it isnot required to input particular information into the shutter device,thus preventing an increase in required information amount. Furthermore,it becomes unnecessary to drive the liquid crystal by the voltage.

Discussion will be given on one embodiment of the light beam reactiveelement. At first, there is a photochromic material which is broughtinto a light beam blocking state by irradiation of light beam. Thisutilizes a phenomenon to cause isolation of, for example, sliver fineparticles by irradiation of light beam and return to become atransparent compound when the light beam is blocked.

It is possible to switch transmission/scattering andtransmission/reflection of light beam by dropwise dispersing in thepolymer a mixture of a material such as azobenzene type polymer causinga photostructural change such as cis-trans structure variation byirradiation of light beam and the liquid crystal. Namely, the shape ofthe material is varied due to the photostructural change, to vary thealignment condition of the liquid crystal and vary a difference inrefractive index between the liquid crystal and the polymer forswitching transmission and scattering. Furthermore, it is also clearthat reflection and transmission by Bragg reflection can be switched byforming the liquid crystal mixture layer and the polymer layer in alaminated manner.

It is also effective to dropwise disperse, in the polymer, a materialcontaining a liquid crystal, nematic-isotropic phase transitiontemperature of which is varied due to structural variation ortemperature variation by irradiation of light beam. In the nematicphase, the light beam is scattered due to birefringence of the material.On the other hand, in the isotropic phase, birefringence is eliminatedso that the light beam becomes transparent. Furthermore, it is alsoclear that reflection and transmission by Bragg reflection can beswitched by forming the liquid crystal mixture layer and the polymerlayer in a laminated manner.

Although the present invention has been illustrated and described withrespect to the preferred embodiments thereof, it should be understood bythose skilled in the art that the present invention is not limited tothe specific embodiments set out above, and that various modificationsand alternations can be added thereto without departing from the spiritand scope of the present invention.

(First Embodiment of Head-Mount Display Device)

FIG. 60 is a perspective view showing a schematic construction of afirst embodiment of a head-mount display device according to the presentinvention, and FIG. 61 is a plan view of the device of FIG. 60, on aplane including eyes of an observer.

In FIGS. 60 and 61, reference numerals 411R and 411L denotetwo-dimensional display devices such as a CRT device, a liquid crystaldisplay device, an EL display device, a plasma display device, a laserscanning type depiction device and a projection type display device.Reference numerals 412R and 412L denote varifocal lenses such as liquidcrystal lens. Reference numerals 413R and 413L are control devices whichcontrols the two-dimensional display devices 411R and 411L and thevarifocal lenses 412R and 412L. Reference numerals 414R is a right eyehead-mount display device which comprises the two dimensional-displaydevice 411R, the varifocal lens 412R and the control device 413R.Reference numeral 414L is a left eye head-mount display device whichcomprises the two-dimensional display device 411L, the varifocal lens412L and the control device 413L. Reference numeral 415R denotes righteye; 415L, a left eye; 416R and 416L, display images; 417, a virtualimage; and S, a partition.

The varifocal lens in the head-mount display device is the opticaldevice set forth above in detail.

As shown in FIGS. 60 and 61, the first embodiment of the head-mountdisplay device comprises the right eye head-mount display device 414Rincluding the two-dimensional display device 411R, the varifocal lens412R and the control device 413R; and the left eye head-mount displaydevice 414L including the two-dimensional display device 411L, thevarifocal lens 412L and the control device 413L, similarly to the righteye head-mount display device 414R. The right eye head-mount displaydevice 414R is worn on the right eye 415R and the left eye headmountdisplay device 414L is worn on the left eye 415L, respectively.

With the construction set forth above, when a display image 416R of thetwo-dimensional display device 411R is viewed by the right eye 415Rthrough the varifocal lens 412R and a display image 416L of thetwo-dimensional display device 411L is viewed by the left eye 415Lthrough the varifocal lens 412R, a virtual image 417 is formed. If thefocal lengths of the varifocal lenses 412R and 412L are varied, thedepth position of the virtual image is varied as shown in FIG. 62, tothus form another virtual image 418. As shown in FIG. 63, athree-dimensional image can be expressed as an aggregate oftwo-dimensional images sampled in the depth direction (hereinafterreferred to as “depth sampled image”).

The depth sampled images are displayed in sequence on thetwo-dimensional display devices 416R and 416L, and then, the controldevices 413R and 413L varies the focal lengths of the varifocal lenses412R and 412L in conformity to the displayed images. Thus, thethree-dimensional image can be expressed as an aggregate of the sampledimages to realize a varifocal type three-dimensional display device.

In the first embodiment set forth above, the virtual image is varied inthe depth direction, in practice. Therefore, discrepancy betweenaccommodation and the binocular disparity or convergence, which has beencaused in the conventional method, can be avoided. Accordingly, it ispossible to satisfy accommodation, binocular disparity, convergence asvisual cues to depth perception in three-dimensional view, to thusrealize a natural three-dimensional view.

In the first embodiment, as the focal lengths (including positive andnegative) of the varifocal lenses 412R and 412L are made smaller, theposition of the virtual image in the depth direction is more distantfrom the eyes, and the images displaced on the two-dimensional displaydevices 416R and 416L are enlarged accordingly. In order to make thesize of the virtual image constant, the size of the displayed image ofthe two-dimensional display devices 416R and 416L has to be variedcorresponding to motion of the focal lengths of the varifocal lenses412R and 412L.

Since, with this nature, the visual field covered by the two-dimensionaldisplay device becomes greater as the length from the eyes becomeslonger, it becomes possible to realize a natural condition similar tothe visual field of the human being.

Furthermore, since the number of, for example, pixels or display linesof the two-dimensional display devices 416R and 416L are not varied, asize of the pixel or a width of the display line becomes greater as adistance of the virtual image from the eyes becomes longer. However,since the visual angle from the eye is not changed, definition of theimage which the human being feels, will be held unchanged.

FIG. 64 is a graph illustrating a relationship between visual cues ofdepth perception and depth perceptivity, and shows depth perceptivityapproximated from measured and calculated values with respect torespective three-dimensional sense factors.

FIG. 65 is a graph illustrating the correspondence and allowable rangeof convergence and accommodation. A central solid line at 45° representsthat the convergence and accommodation are completely corresponded. Theregion in the vicinity of the 45° solid line is a range allowable atcertain focal depth. Although the range is slightly different sincevisual acuity (0) and blur detection ability (δ) are employed asallowable levels, it is quite narrower than a binocular fusional area ofstereoscopy. The outer curve shows a sort of binocular fusion limits;the solid line with black dots represents maximum binocular fusion imagelimit (allowable convergence limit); the dotted line shows a range inwhich a fusion image condition is established from twin image condition(fusion limit); and the broken line represents binocular fusion limit atan image display time of 0.5 sec. (convergence limit of display at ashort period of 0.5 sec.). With respect to the moving picture,long-period observation may cause considerable fatigue by thethree-dimensional effect out of the range indicated by the broken line.Reference symbol MW represents or convergence angle; and D, a diopter.

According to the present invention, when the depth sampling is employed,it becomes necessary to define the number of sampling. Here, theaccommodation of human eyes is effective only when the visual range isshort (less than or equal to 2 m), as shown in FIG. 64. Moreover,resolution in the depth direction is relatively as low as 1/10 or moreof the visual range. There is also an allowable range of the convergenceangle, as illustrated in FIG. 65. Therefore, in practice, a naturalthree-dimensional image can be realized if the number of the depthsampling ranges from 20 to 40.

Although, in the first embodiment, the three-dimensional image isrealized as an aggregate of the depth sampled images. It is clear thatthe three-dimensional image can be realized in various other ways, e.g.,an aggregate of lines.

It should be noted that the construction shown in FIGS. 60 and 61 is oneexample which makes the device compact by bending the optical pathemploying a mirror, lens, prism or the like.

(Second Embodiment of Head-Mount Display Device)

FIG. 66 shows a schematic construction of a second embodiment of thehead-mount display device according to the present invention. In FIG.66, reference numerals 421R and 421L denote two-dimensional displaydevices; 422R and 422L, varifocal lenses, 423R and 423L, controldevices; 424R and 424L, deflection devices; 425R and 425L, displayimages; and 417, a virtual image. Examples of the deflection devices424R and 424L are a liquid crystal prism, a movable mirror, a liquidprism and the like. The second embodiment is adapted to easily establishthe natural correspondence between the convergence angle andaccommodation.

The second embodiment of the head-mount display device comprises thetwo-dimensional display devices 421R and 421L, the varifocal lenses 422Rand 422L and the control devices 423R and 423L for controlling thedevices 421R and 421L and the lenses 422R and 422L, as shown in FIG. 66.

In the head-mount display device, in order to generate a largeconvergence angle as the depth position of a three-dimensional imageapproaches eyes, it is necessary to make the right and left imagesobserved by the right and left eyes closer to the midpoint between boththe eyes. Since, in the first embodiment of the head-mount displaydevice, this operation is performed by fusing the two-dimensionaldisplay devices 421R and 421L, the display images are displayed closertoward the midpoint between the right and left eyes. Therefore, controlof the display images of the two-dimensional display devices 421R and421L becomes quite complicated. Additionally, if the convergence angleis varied significantly, it becomes necessary to make thetwo-dimensional display device greater in the lateral direction beyondthe visual field.

To the contrary, in the second embodiment, the right and left images inthe lateral direction for forming the convergence angle are moved by thedeflection devices 424R and 424L. Namely, the operations of thetwo-dimensional display devices 421R and 421L and the varifocal lens422R and 422L are similar to those of the first embodiment. However, asthe focal lengths of the varifocal lenses 422R and 422L become longerand the virtual images of the display images 425R and 425L of thetwo-dimensional display devices 421R and 421L approach closer to theright and left eyes in the depth direction, the display images of thetwo-dimensional display devices 421R and 421L approach toward the centerposition midpoint between the right and left eyes by the deflectiondevices 424R and 424L.

Consequently, in the second embodiment of the head-mount display device,the two-dimensional display and the convergence angle control can beindependently controlled with ease. Further, the entire screen surfacesof the two-dimensional display devices 421R and 421L can be effectivelyused. Namely, the convergence angle becomes small when the virtual image417 is farther from the right and left eyes, while the convergence anglebecomes greater when the virtual image 417 is closer to the right andleft eyes. Thus, the convergence angle and accommodation can be easilysatisfied.

Although in the second embodiment, the deflection devices 424R and 424Lare located closer to the two-dimensional display devices 421R and 421Lthan the varifocal lens 422R and 422L. However, it is clear that thesame advantageous result can be achieved even in the case where thedeflection devices 424R and 424L are located closer to the right andleft eyes than the varifocal lenses 422R and 422L.

Moreover, although in the second embodiment as shown as FIG. 66, thedeflection devices 424R and 424L and the varifocal lenses are providedseparately, the same advantageous result can be, achieved even in thecase of variable optical devices 426R and 426L in which the deflectiondevices 424R and 424L and the varifocal lenses are integrated, as shownin FIG. 67. Thus, such construction is quite effective in making thedevice compact.

INDUSTRIAL APPLICABILITY

As set forth above, the optical device according to the presentinvention enables high speed operation by varying the frequency of thevoltage to be applied to the variable refractive index material so as tovary its refractive index and by varying the optical property of thedevice formed together with the transparent material having the desiredcurved surface configuration. Furthermore, since the force of exerted bythe electric field can be used constantly, the operating speed can bemade higher by increasing the strength of the electric field.

In the optical device according to the present invention, the forceexerted by the electric field can vary the refractive index of thevariable refractive index material. Moreover, since the transparentelectrodes are not provided on the transparent material layer on theside of the variable refractive index material, the influence of thesurface configuration of the transparent material layer becomes small,to easily achieve uniformity of the variation in optical property.

Since the transparent electrodes are not provided on the transparentmaterial layer on the side of the variable refractive index material inthe optical device according to the present invention, it becomesunnecessary to form a film on a portion having a complex configuration,to thus facilitate fabrication. Furthermore, since the transparentelectrodes are not provided on the transparent material layer on theside of the variable refractive index material, the distance between theelectrodes can be maintained substantially equal. Additionally, sincethe transparent material layer is constantly present between thetransparent electrodes, degradation in insulating, property orshort-circuiting can be successfully avoided.

Further, in the optical device according to the present invention, therefractive index of the variable refractive index material isperiodically varied according to the frequency of each voltage to selectthe intermediate value, thereby achieving sequential variation of theoptical property.

The optical device according to the present invention can maintain thedesired refractive index by utilizing the state maintainingcharacteristics of the variable refractive index material while thevoltage supply is stopped. Therefore, it becomes possible to vary therefractive index at a high speed but in a non-periodic manner.

The optical device according to the present invention sequentiallyvaries the refractive index according to a voltage ratio of the voltageshaving different frequencies in superimposing manner and to be appliedto the variable refractive index material, so as to vary the opticalproperty of the device sequentially, enabling high-speed driving withsequential variation, unlike the conventional device which cannot bedriven at a high speed. Furthermore, since the force exerted by theelectric field can be constantly used, the further speeding-up can beachieved by increasing the strength of the electric field.

The optical device according to the present invention can maintain thedesired refractive index by utilizing the state maintainingcharacteristics of the variable refractive index material while thevoltage supply is stopped. Therefore, it becomes possible to vary therefractive index at a high speed but in a non-periodic manner.

The optical device according to the present invention can achieve auniform alignment condition in a wide domain region under the drivingcondition where the liquid crystal is aligned in parallel to thealignment layer. Thus, variation of the refractive index of the liquidcrystal can be efficiently transferred to the incident light beam. Inaddition, scattering of the light beam caused by the random orientationof the liquid crystal and the resultant cloudiness can be successfullyavoided.

Furthermore, the optical device according to the present invention isconstructed in such a manner as to reflect the light beam, efficientlytransferring the variation of the refractive index of the variablerefractive index material to the incident light beam. Further, variousfunctions can be realized irrespective of the polarizing condition ofthe incident light beam. Therefore, various optical devices, such as anactive mirror and a half mirror capable of varying the optical propertycan be realized.

In addition, the optical device according to the present invention hasthe driving device which can constantly supply the voltage having theamplitude greater than or equal to the voltage amplitude, at which theliquid crystal is effectively and statistically aligned in the frequencyof the voltage, to thus generate an electrically hydrodynamic motion inthe molecules of the liquid crystal. Consequently, the direction of themolecules of the liquid crystal is oscillated between the state wherethe molecules of the liquid crystal are aligned perpendicularly or inparallel to the electrode and the state where the molecules of theliquid crystal are slightly inclined in synchronism with a frequencytwice as high as that of the applied voltage. Therefore, the opticaldevice according to the present invention can vary the optical propertyat a high speed, sequentially, periodically and uniformly. Furthermore,since it becomes unnecessary to form the film into complicated surfaceconfiguration, production can be facilitated.

The three-dimensional display device according to the present inventiondrives the imaging point shifting portion on the bases of the drivingsignal generated by the driving portion, and the synchronizing portionupdates the two-dimensional images to be displayed on the displayportion sequentially in a predetermined order on the basis of the outputfrom the driving portion. Therefore, position of the two-dimensionalimage to be the displayed on the display portion can be varied in thedirection of the eyes of the observer so that the observer maythree-dimensionally view the two-dimensional images on thetwo-dimensional plane displayed on the display means.

The three-dimensional display device according to the present inventioncan satisfy the visual cues to depth perception in three-dimensionalview such as binocular disparity, convergence, accommodation andmovement parallax without using any eyeglasses and display the movingpicture which can be re-written electrically.

Otherwise, the phantom three-dimensional display device according to thepresent invention is additionally provided with the shutter device whichcan switch in timewise and/or spacewise among the light beamtransmitting state, light beam scattering state and light beamreflecting state. In the phantom three-dimensional display device, theshutter device is disposed at the position including the position wherethe phantom three-dimensional image is reproduced. Thisthree-dimensional display device activates the function for blocking orscattering the light beam of the shutter elements of the shutter devicewhen the phantom three-dimensional image at the backside as viewed fromthe observer is reproduced. As a result, many of the visual cues todepth perception in three-dimensional view can be satisfied and thenatural three-dimensional image without any phantom phenomenon can beelectrically reproduced in the form of the moving picture.

The head-mount display device according to the present invention,comprising the two-dimensional devices and the varifocal lenses are wornon the right and left eyes of the human being so that the display imagesof the two-dimensional display devices are observed through thevarifocal lenses, and the focal lengths of the varifocal lens are variedfor varying the position of the virtual image of the display image ofthe two-dimensional display device in the depth direction. As a result,it is possible to reproduce the three-dimensional image without anydiscrepancy in visual cues to depth perception in three-dimensional viewsuch as binocular disparity, convergence and accommodation at a highspeed in an electrically rewriteable manner.

1. A three-dimensional display device comprising: a phantomthree-dimensional display device for displaying a phantomthree-dimensional image comprised of an aggregation of depth sampledimages in a depth direction; and a shutter device having a plurality ofshutter elements for controlling a light transmittance of the displayedphantom three-dimensional image and having control means for controllingselection of the shutter elements, wherein the shutter elements arearranged such that a position of each shutter element is consistent witha position at a portion of the phantom image in the depth direction;wherein a plurality of the shutter elements are controlled at the sametime such that each shutter element is set to an opening state or aclosing state partially at one moment, and wherein one portion of thephantom image according to a position of the shutter element in thedepth direction becomes a transparent state partially when the shutterelement is set to the opening state partially and another portion of thephantom image according to a position of the shutter element in thedepth direction becomes a non-transparent state partially when theshutter element is set to the closing state partially.
 2. Athree-dimensional display device as set forth in claim 1, wherein saidshutter elements are two-dimensionally divided in a plane perpendicularto the depth direction of the displayed phantom three-dimensional image,and each of divided regions is controlled independently by the controlmeans.
 3. A three-dimensional display device as set forth in claim 1,wherein a predetermined shutter element lowers a light transmittance ina region of the displayed phantom three-dimensional image at eachposition of the shutter elements controlled by the control means whenthe displayed phantom three-dimensional image is located in the depthdirection in a time division manner.
 4. A three-dimensional displaydevice comprising: a phantom three-dimensional display device fordisplaying a phantom three-dimensional image comprised of an aggregationof depth sampled images; and a shutter device having a plurality ofshutter elements for controlling a light transmittance, wherein theshutter elements are arranged at positions where the depth sampledimages are displayed in a depth direction, and each of the shutterelements are controlled in a time division manner respectively so as tovary the light transmittance, and wherein the material of said shutterelement is one or combination of guest-host type liquid crystalcontaining diachronic dye having a different light beam absorptiondepending upon an orientation of molecules and liquid crystal havingdielectric constant anisotropy, polymer dispersion type liquid crystalcontaining droplet-like liquid crystal in polymer, polymer dispersedliquid crystal containing a polymer network in liquid crystal, aholographic polymer dispersed liquid crystal having a layer structure ofpolymer dispersed liquid crystal containing droplet like liquid crystalin polymer and polymer, a holographic polymer dispersed liquid crystalhaving a layer structure of said polymer dispersed liquid crystalcontaining a polymer network in the liquid crystal and polymer, and apolymer dispersed liquid crystal wherein said liquid crystal in saidpolymer dispersed liquid crystal is said guest-host type liquid crystal.5. A three-dimensional display device comprising: a phantomthree-dimensional display device for displaying a phantomthree-dimensional image comprised of an aggregation of depth sampledimages; and a shutter device having a plurality of shutter elements forcontrolling a light transmittance, wherein the shutter elements arearranged at positions where the depth sampled images are displayed in adepth direction, and each of the shutter elements are controlled in atime division manner respectively so as to vary the light transmittance,and wherein said phantom three-dimensional display device is constructedwith a two-dimensional image display device and a varifocal opticaldevice.
 6. A three-dimensional display device comprising: a phantomthree-dimensional display device for displaying a phantomthree-dimensional image comprised of an aggregation of depth sampledimages; and a shutter device having a plurality of shutter elements forcontrolling a light transmittance, wherein the shutter elements arearranged at real positions according to depth positions where the depthsampled images are displayed as optical real images, and the shutterelements are photoreactive elements for lowing a light transmittance ina region of the depth sampled images at the positions of the shutterelements according to the real positions.
 7. A three-dimensional displaydevice as set forth in claim 6, wherein a material of said photoreactiveelement is one of a photochromic material, a material consisting of amaterial causing a photostructural change and liquid crystal, and amaterial having a nematic-anisotropic phase transition temperature to bevaried by photostructural change.
 8. A three-dimensional display deviceas set forth in claim 6, wherein said phantom three-dimensional displaydevice includes a two-dimensional image display device and a varifocaloptical device.
 9. A head-mount display device comprising: two displaydevices corresponding to left and right eyes wherein each deviceincludes a two-dimensional display device and an optical device having avariable focal length; and a control device for controlling saidtwo-dimensional display device, said optical device having a variablefocal length and a deflection device for varying a direction of a lightincident to said optical device, wherein the control device controls thedisplay and optical devices so that the focal lengths of the opticaldevice are focused on the positions of the depth sampled images, andcontrols said optical device in such a way that when the image is movingcloser to the eyes according to a change of the focal length, theoverall display image of said two-dimensional display device isdeflected to be closer toward the center between the left and righteyes.
 10. A head-mount display device comprising: two display devicescorresponding to left and right eyes wherein each device includes atwo-dimensional display device and an optical device having a variablefocal length; and a control device for controlling said two-dimensionaldisplay device and said optical device having a variable focal length,wherein the control device controls the display and optical devices sothat the focal lengths of the optical device are focused on thepositions of the depth sampled images, wherein said optical device has atransparent material, a layer including a variable refractive indexmaterial, and at least a pair of transparent electrodes for sandwichingsaid layer, and wherein the transparent material is comprised of one offorms of a fixed focus lens shape, a fixed prism shape, and a shapewhere the fixed deflection mechanism is incorporated into the fixedfocus lens.
 11. A head-mount display device as set forth in claim 10,wherein said variable refractive index material is liquid crystal havingdielectric constant anisotropy and refractive index anisotropy.
 12. Ahead-mount display device as set forth in claim 11, wherein saidvariable refractive index material is liquid crystal having dielectricconstant anisotropy and refractive index anisotropy, and beingdual-frequency liquid crystal having a different physical propertyhaving a different sign of a difference in a dielectric constantcorresponding to orientation of the liquid crystal molecules betweendifferent frequencies f1 and f2.
 13. A head-mount display device as setforth in claim 10, wherein said variable refractive index material ispolymer dispersed liquid crystal, and the droplet size of the liquidcrystal, or the droplet size of the polymer is smaller than a wavelengthof visible light.
 14. A head-mount display device as set forth in claim10, wherein said fixed focus lens is spherical or non-spherical singlelens or fresnel lens.
 15. A head-mount display device as set forth inclaim 10, wherein said fixed prism is simple prism or a multi-prismhaving an array of a plurality of fine prisms.
 16. A head-mount displaydevice as set forth in claim 10, the form where said fixed deflectionmechanism is incorporated in to said fixed focus lens is in the form ofincreasing or decreasing an angle formed by a spherical or non-sphericalsimple lens or a fresnel lens and an optical axis.
 17. A head-mountdisplay device, comprising: two display devices corresponding to leftand right eyes wherein each device includes a two-dimensional displaydevice and an optical device having a variable focal length; and acontrol device for controlling said two-dimensional display device andsaid optical device having a variable focal length, wherein the controldevice controls the display and optical devices so that the focallengths of the optical device are focused on the positions of the depthsampled images, said display devices are mounted to left and right eyes,and said control device synchronously drives said two-dimensionaldisplay device and said optical device to perform three-dimensionaldisplay, and wherein said optical device has a transparent material, alayer including a variable refractive index material, and at least apair of transparent electrodes for sandwiching said layer, and whereinsaid control device sequentially applies voltages V1 to VN havingprimary frequencies f1 to fN (N≧2) to said transparent electrodes for apredetermined period of time and at a predetermined interval.